-NRLF 


RUBBER 
MANUFACTURE 


THE  CULTIVATION,  CHEMISTRY,  TESTING,  AND 
MANUFACTURE  OF  RUBBER,  WITH  SECTIONS 
ON  RECLAMATION  OF  RUBBER  AND  THE 
MANUFACTURE  OF  RUBBER  SUBSTITUTES 


By 

H.  E.  SIMMONS 

a 

Professor  of  Chemistry,  Municipal  University  of  Akron,  Ohio 


ILLUSTRATED 


NEW  YORK 

D.  VAN  NOSTRAND  COMPANY 

EIGHT  WARREN  STREET 
1921 


Copyright,  1921 

by 
D.  VAN  NOSTRAND  COMPANY 


Printed   in   the   United   States  of  America 


TS/210 


TO 

MY     PARENTS 

who  by  their  sacrifices  made  it 

possible  for  me  to  obtain 

an  education. 


6S7034 


PREFACE 

The  author  has  attempted  to  give  in  this  volume  a  brief  but  com- 
plete survey  of  the  Rubber  Industry.  The  production  of  crude  rub- 
ber, including  the  methods  in  use  for  collecting  both  wild  and  plan- 
tation rubber,  are  carefully  described  as  well  as  the  processes  in  use 
for  coagulating  and  curing  the  crude  rubber. 

The  manufacture  of  numerous  inorganic  fillers  and  their  proper 
use  in  rubber  compounding  are  given  in  full  as  well  as  the  various 
processes  employed  for  fabricating  rubber  goods.  The  apparatus 
used  in  all  parts  of  the  industry  is  fully  illustrated  and  described. 

The  chemical  and  physical  properties  of  the  latex  and  rubber, 
including  the  production  of  synthetic  caoutchouc,  are  fully  discussed. 
Chapters  have  also  been  included  on  the  chemical  analysis  and  phys- 
ical testing  of  rubber  and  its  compounds  and  the  various  theories  of 
vulcanization. 

While  the  attempt  has  been  made  to  present  the  technical  fea- 
tures of  the  subject  in  a  scientific  manner  so  that  the  volume  will  be 
of  value  to  students  of  this  subject,  it  is  believed  that  a  large  part  of 
the  volume  will  be  of  interest  to  the  non-technical  reader.  Both 
classes  of  readers  will  no  doubt  be  interested  in  the  attempts  to  point 
the  way  for  the  future  development  of  this  most  important  product. 

H.  E.  S. 
Akron,  Ohio, 

February  1,  1921. 


CONTENTS 


CHAPTER  I 
THE   HISTORY  OF  CAOUTCHOUC 1 

CHAPTER  II 

RUBBER  OF  THE  AMAZON  BASIN 4 

Varieties?.     Methods  of  Tapping.     Coagulating  Latex. 

CHAPTER  III 

AFRICAN.  RUBBERS,  INCLUDING  THOSE  FROM  MADAGASCAR.     11 

Varieties.     Coagulation.     Obtaining  and  Coagulating  Latex  from  Vines. 

CHAPTER  IV 

CENTRAL  AMERICAN  RUBBERS    18 

CHAPTER  V 

RUBBER  PLANTATIONS  AND  THEIR  DEVELOPMENT 26 

Ceylon.     Malaya.     Planting  Kubber    Trees.     Cultivating    the     Land.     Tapping    the 

Trees.     Coagulating  the  Latex.  Tree  Diseases  and  Other  Pests.     Other  Varieties  of  Rub- 
ber Trees. 

CHAPTER  VI 

DISCUSSION   OF   COLLOIDS    37 

Brownian  Movements.  Characteristics  of  Sols.  Surface  Tension.  Cntaphoresis  and 
Electro-endosmos. 

CHAPTER  VII 

COLLOIDAL  ACTION   OF   CRUDE   RUBBER  AND   ITS   APPLICA- 
TION IN  RUBBER  MANUFACTURE    43 

Preservation  of  Latex.  Coagulation  by  Chemicals.  Application  of  Colloidal  Chem- 
istry. 

CHAPTER  VIII 
DIFFERENT  MEANS  OF  COAGULATION    47 

CHAPTER  IX 

THEORY  OF  THE  CONSTITUTION  OF  RUBBER 55 

CHAPTER  X 

SYNTHETIC    CAOUTCHOUC    59 

CHAPTER  XI 

CHEMICAL  AND  PHYSICAL  TESTING  OF  CRUDE  RUBBER 64 

Washing  Loss.  Determination  of  Moisture.  Estimation  of  Resin.  Determination  of 
Ash.  Determination  of  Nitrogen.  Determination  of  Insoluble  Matter.  Determination  of 
Rubber.  Viscosity  of  Rubber.  Specific  Gravity.  Sun  Cracking.  Vulcanizing  Test. 


CHAPTER  XII 

THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 71 

Inorganic  Accelerators.  Barytes.  Aluminum  Compounds.  Talc.  .Silicon  Oxides. 
Asbestos.  Calcium  Carbonates.  Sulphides.  Magnesium  Carbonate.  White  Pigment.  Zinc 
Oxide.  Zinc  Sulphides.  Lithopone.  Barytes  and  Kaolin.  Red  Pigments.  Golden  and 
Crimson  Antimony.  Iron  Sesquioxide.  Rouge.  Red  Ochre.  Red  Hematite.  Vermilion. 
Black  Pigments.  Lampblack.  Bone  Black.  Gas  Carbon.  Black  Hypo.  Graphite.  Lead 
Sulphide.  Yellow  Pigments.  Yellow  Ochre.  Chrome  Yellow.  Cadmium  Yellow.  Arsenic 
Trisulphide.  Yellow  Dyestuft's  Used.  Green  and  Blue  Pigments.  Chrome  Green.  Rin- 
mann's  Green.  Ultramarines.  Prussian  Blue.  Thenard's  Blue. 


THE  MANUFACTURE  AND  USE  OF  ORGANIC  ACCELERATORS.  .     85 
Action  of  Catalysis.    Accelerators. 

CHAPTER  XIV 
THE  MANUFACTURE  AND  USE  OF  RUBBER  SUBSTITUTES 92 

CHAPTER  XV 

THEORIES  OF  VULCANIZATION   98 

Weber's  Theory.  Oswald's  Theory.  Spence's  Experiment.  Reversibility  of  Vulcani- 
zation Process.  Migration  of  Sulphur  in  Rubber.  Researches  by  Loewen.  Vulcanization 
and  Viscosity.  Ostromislensky's  Theory. 

CHAPTER  XVI 

METHODS  OF  RECLAIMING  RUBBER   105 

Devulcanization  Processes. 

CHAPTER  XVII 

PREPARATION  OF  CRUDE  RUBBER  FOR  MANUFACTURING Ill 

The  Receiving  Room.     Washing.     Drying.     Mixing  Mills. 

CHAPTER  XVIII 

THE  PRINCIPLES  OF  COMPOUNDING  117 

Tensile  Strength.    Elasticity.    Ageing  Qualities.    Colors.    Specific  Gravity.   Scorching. 

CHAPTER  XIX 

CHEMICAL  ANALYSIS  OF  MANUFACTURED  RUBBER 123 

Procedure  of  Analysis.  Determination  of  Organic  Content.  Determination  of  Sul- 
phur. Barium  Sulphate  Troubles.  Determination  of  Mineral  Oil,  Vaseline  and  Paraffin. 
Determination  of  Rubber  Substitute.  Determination  of  Rubber  Content.  Determination 
of  Sulphur.  Analysis  of  Mineral  Matter.  Determination  of  Carbon  or  Graphite. 

CHAPTER  XX 

PHYSICAL  TESTING  OF  COMPOUND  SAMPLES 132 

Tensile  Strength.  "  Grain."  Hardness.  Hysteresis.  Specific  Gravity.  Artificial  Age- 
ing Tests.  Light  Tests.  Weather  Exposure  Tests.  Dielectric  Tests.  Viscosity  Tests. 
Friction  Tests.  Barbeque  Test. 

APPENDIX 

THE    LABORATORIES    AND    EQUIPMENT    OF    THE    MUNICIPAL 

UNIVERSITY  OF  AKRON 147 

The  Rubber  Laboratory  Equipment.  Brief  Description  of  the  Course.  Two  Industrial 
Fellowships. 


CHAPTER  I 


The  History  of  Caoutchouc 


Before  starting  this  series  of  chap- 
ters, it  seems  to  me  both  necessary 
and  interesting  to  take  a  brief  glance 
into  history  and  obtain  a  little  knowl- 
edge as  to  when  and  by  whom  this 
important  article  of  commerce  was 
first  found.  It  is  my  purpose  to 
deal  principally  with  the  rubber 
industry  as  it  is  at  the  present  time, 
yet  to  omit  mentioning  the  discovery 
of  this  substance  would  be  unfair 
to  the  pioneers,  and  would  also  render 
a  work  of  this  nature  incomplete. 

It  has  been  stated  that  the  first 
reference  to  rubber  occurs  in  the 
work  of  a  Spanish  writer  of  Madrid 
in  1536,  but  M.  L.  Tillier  points  out 
that  P.  Martyr  d'Angliera  in  1525 
published  a  description  of  some  rub- 
ber playing  balls  seen  by  him  in 
Mexico. 

Another  Spanish  writer  describes 
the  same  article  as  made  "  from  a 
black  resin,  obtained  from  a  tree 
called  by  the  natives  Ulaquhuil. ' '  In 
this  connection  it  will  be  well  to  state 
that  in  parts  of  Mexico  and  Central 
America  even  to-day  the  Castilloa 
elastica  is  known  as  the  Ule  tree. 

According  to  Morris,  the  first 
record  of  india-rubber  was  made  soon 
after  the  discovery  of  the  New  World 
by  Columbus.  The  Old  World  rub- 
bers wrere  still  unknown.  Columbus, 
on  his  second  voyage,  noticed  the 
inhabitants  of  Hayti  playing  with  a 
ball  made  from  the  resin  of  a  tree. 
It  is  interesting  to  note  that  the  game 
which  the  natives  played  with  these 
balls  is  still  played  in  these  regions 
and  in  fact,  modern  explorers  have 
become  aware  of  the  presence  of  rub- 
ber yielding  trees  simply  by  observ- 
ing that  this  game  wras  being  played. 
Antonio  de  Herrera  Tordesillas,  a 
Spanish  historian  in  1601,  in  his 
"  General  History  of  the  Voyages 


and  Conquests  of  the  Castillians  " 
while  speaking  of  the  conquests^  in 
Mexico,  mentions  certain  trees  which, 
when  punctured,  yield  a  milk  which 
becomes  converted  into  a  gum  with 
a  very  fine  smell. 

Father  Xavier  de  Charleroix  of 
the  Society  of  Jesus,  1682-1761,  de- 
scribes the  Batoa,  a  species  of  ball 
of  a  solid  matter  but  extremely 
"  porous  and  light.  It  soars  higher 
than  other  balls,  falls  to  the  ground 
and  rebounds  higher  than  the  level 
of  the  hand  which  it  quitted.  It  falls 
to  the  ground  and  rebounds  once 
more  although  not  to  such  a  height 
this  time,  and  the  height  of  the  bound 
is  gradually  diminished." 

Whatever  the  date  may  be  which 
marks  the  first  recognition  of  this 
important  article  in  civilization,  we 
at  least  must  give  credit  to  the  Span- 
ish and  Portuguese  explorers  of  the 
West  Indias  as  being  the  first  to  ob- 
serve it  and  record  it  in  their  litera- 
ture. 

The  French  were  the  first  to  make 
any  scientific  study  of  rubber  bear- 
ing plants.  The  Academy  of  Science 
of  Paris  in  1731  sent  an  expedition 
to  South  America  under  the  guidance 
of  La  Condamine  and  Bougner.  In 
1736,  La  Condamine  sent  back  to  the 
Academy  a  resinous  mass  under  the 
name  of  "  caoutchouc  "  and  this 
information : 

"  There  grows  in  the  province  of  Es- 
meraldas.  a  tree  called  by  the  natives  of 
the  country  '  Heve  ' ;  there  flows  from  it. 
by  simple  incision,  a  liquor,  which 
hardens  gradually  and  blackens  in  the 
air.  The  inhabitants  make  flambeaux  of 
it,  which  burns  very  well  without  wicks, 
and  gives  rather  of  a  fine  light.  .  .  . 
In  the  province  of  Quito. -sheets  of  linen 
are  coated  with  it.  and  are  used  for  the 
same  purpose  as  we  use  waxcloth.  .  .  . 
The  same  tree  grows  along  the  banks  of 
the  Amazon  and  the  Mainas  Indians  call 


RUBBER   MANUFACTURE 


the  resin  which  they  extract  from  it 
'  cjihuchu  '  (pronounce  caoutchouc).  They 
make  boots  of  it,  which  do  not  draw 
water,  which  after  heing  blackened  by 
J^ing  held.in.tjie  s.njoke,  have  all  the  ap- 
iwja-rjwice  o£.'l(£itj<er:  TThey  coat  earthen 
m'ofds  in'ttfe  slfape'of.a  bottle  with  it, 
«ud^.\y4>ej>kthe •re.^ii^haV- hardened,  they 
>.§iJ3l^^t)i&.Jnt#4  .45<J*&orpe  out  the  pieces 
through  the  neck  and  mouth;  thus  they 
get  a  nonfragile  bottle,  capable  of  con- 
taining all  kinds  of  liquid." 

He  also  mentions  a  peculiar  use 
which  one  of  the  tribes  made  of 
this  india-rubber : 

"  The  use  which  is  made  of  this  resin 
by  the  Omaguas,  in  the  middle  of  the 
American  continent,  on  the  banks  of  the 
Amazon,  is  still  more  singular ;  they 
make  bottles  of  it  in  the  shape  of  a  pear, 
to  the  neck  of  which  they  attach  a  fluted 
piece  of  wood.  By  pressing  the  bottles 
the  liquid  which  they  contain  is  made  to 
flow  out  through  the  fluted  piece  of  wood, 
and  by  this  means  these  bottles  become 
real  syringes." 

That  is  the  origin  of  the  name 
given  by  the  Portuguese  to  the  tree 
which  yields  this  resin,  Pao  de 
Ciringa  (syringe-wood),  and  of  ser- 
ingueiros  to  the  resin  collectors. 

At  this  point  La  Condamine  had 
to  give  up  his  pursuit  of  this  peculiar 
substance  and  devote  his  time  to  his 
own  profession,  for  he  was  a  doctor 
of  medicine  and  an  eminent  natur- 
alist. At  this  time  he  came  in  touch 
with  Fresneau,  the  French  engineer 
located  at  Cayenne,  who  seemed  to 
grasp  the  importance  of  this  sub- 
stance and  took  up  the  work  where 
La  Condamine  had  abandoned  it. 
After  great  labor  and  hardship  he 
succeeded  in  finding  these  trees  and 
noticing  how  the  natives  proceeded 
to  obtain  this  resin,  he  sent  the  fol- 
lowing communication  to  La  Con- 
damine : 

"  They  commence  by  washing  the  foot 
of  the  tree ;  then  they  make  with  a  bill- 
hook, longitudinal  but  rather  oblique 
incisions  which  should  penetrate  the 
whole  thickness  of  the  bark,  taking  care 
to  make  them,  one  above  another,  so  that 
the  flow  from  the  top  incision  falls  into 
the  one  underneath,  and  so  on  until  the 
last  one  at  the  bottom  of  which  a  leaf 
of  the  Balizier  (an  American  reed)  is 
placed,  which  is  made  to  hold  the  liquid 
by  potter's  earth,  so  as  to  lead  the  juice 
into  a  vessel  placed  at  the  foot  of  the 
tree. 

"To  utilize  the  milky  juice  of  the  trees 
which  I  have  mentioned,  a  mold  is  made 
of  potter's  earth,  according  to  the  shape 
of  the  vessel  which  it  is  intended  to  make, 


and,  to  hold  it  more  conveniently,  a 
piece  of  stick  is  inserted  in  the  place 
which  is  not  to  be  coated  with  the  milky 
juice.  An  aperture  is  thus  secured 
through  which  the  potter's  earth  may  be 
afterward  expelled,  by  introducing  water 
to  soften  it.  Any  one  mold  being  shaped, 
polished,  and  softened  with  water,  it  is 
coated  all  over  with  milky  juice  by  means 
of  the  fingers,  after  which  this  coating 
is  exposed  to  a  dense  smoke,  where  the 
heat  of  the  fire  hardly  makes  itself  felt, 
keeping  constantly  turning  it,  so  that  the 
juice  may  be  spread  equally  over  the 
mold,  and  taking  good  care  that  the  flame, 
does  not  reach  it,  which  would  cause  the 
milky  juice  to  boil,  and  thus  to  form 
small  holes. 

"  As  soon  as  a  yellow  color  is  seen, 
and  this  first  coating  is  no  longer  tacky 
to  the  fingers,  a  second  layer  is  applied, 
which  is  treated  in  the  same  way,  and 
so  on  with  the  other  coats,  until  it  is 
judged  to  be  sufficiently  thick,  and  then 
it  is  kept  longer  over  the  flame  so  as 
to  evaporate  the  whole  of  the  moisture, 
until  but  the  elastic  resin  remains.  .  .  . 
With  this  juice  and  linen  sheeting,  tar- 
paulins, pump  hose,  divers'  clothing,  bot- 
tles, sacks  for  containing  campaigning 
biscuit,  etc.,  may  be  made,  without  fear 
of  this  material  imparting  any  bad  smell ; 
but  all  of  these  things  can  only  be  exe- 
cuted on  the  spots  where  the  tree  grows, 
as  these  juices  soon  lose  their  fluidity." 

In  1762  the  French  botanist  Fuset- 
Ablet  started  for  Guiana  and  two 
years  later  he  published  "  The  Flora 
of  Guiana,"  and  in  this  he  described 
a  tree  which  he  called  Hevea  Ginjun- 
ensis. 

In  1798  James  Howison  determined 
the  name  of  an  elastic  gum  vine,  the 
species  which  later  on  was  called 
Urceola  elastica.  This  tree  was  the 
chief  source  of  supply  from  the  East 
prior  to  the  introduction  of  that  from 
the  Ficus  elastica.  It  was  discovered 
on  the  island  of  Penang.  While 
clearing  a  way  through  the  jungle 
with  cutlasses,  the  blades  became 
covered  with  a  juice  which  hardened 
and  had  the  appearance  of  india-rub- 
ber. The  source  of  this  juice  was 
found  to  be  a  vine  about  as  thick 
as  a  man's  arm,  which  ran  along  the 
ground  for  great  distances,  rooted 
at  its  joints  and  also  climbed  the 
highest  trees.  It  was  thought  to  be 
a  species  of  Hevea,  with  which  it  is 
often  confused  even  to  this  day.  This 
juice  was  also  used  by  the  natives 
to  waterproof  different  articles. 

It  is  reported  that  in  1755  the  King 
of  Portugal,  having  heard  of  the 


THE  HISTORY  OF  CAOUTCHOUC 


waterproofing  material  of  the  In- 
dians, sent  several  pairs  of  his  royal 
boots  to  Para  in  order  that  they 
might  be  covered  with  rubber. 

Priestley  is  credited  with  having 
given  this  substance  the  recommenda- 
tion to  use  for  effacing  pencil  marks, 
and  from  this  it  was  called  "  india- 
rubber.  ' ' 

"W.  H.  Johnson  gives  us  the  deriva- 
tion of  the  word  caoutchouc  as  com- 
ing from  caucho,  which  in  turn  comes 
from  cao,  meaning  wood,  and  o-chu, 
meaning  to  run  or  weep. 


In  this  work  I  shall  use  the  term 
"  caoutchouc  "  when  reference  is 
made  to  the  pure  hydrocarbon  while 
I  shall  use  india-rubber  as  a  term  for 
the  crude  product  whether  raw  or 
manufactured. 

When  we  realize  that  it  was  toward 
the  end  of  the  eighteenth  century 
before  rubber  was  introduced  into 
Great  Britain  the  wonderful  advance 
made  in  this  length  of  time  makes  it 
impossible  for  us  to  prophesy  what 
the  future  has  in  store- along  this  line. 


CHAPTER  II 
Rubber  of  the  Amazon  Basin 


As  stated  in  Chapter  I,  the  French 
were  the  pioneers  in  obtaining  exact 
information  in  regard  to  the  South 
America  rubbers.  It  was  the  expedi- 
tion of  de  La  Condamine  and  Boug- 
ner,  from  the  Paris  Academy  of 
Science,  in  1731,  that  sent  the  first 
reports  dealing  with  rubber  in  Peru 
and  Brazil  back  to  the  Eastern  World. 

In  1736  de  La  Condamine  sent 
home  samples  of  rubber,  and  referred 
to  the  fact  that  in  the  province  of  the 
Esmeraldas  there  occurred  a  tree 
called  by  the  natives  Hevea,  and  that 
they  obtained  from  it  a  milk  white 
liquid,  which  gradually  hardened  and 
blackened  in  the  air.  He  also  men- 
tioned that  in  the  province  of  Quito 
the  natives  coated  linen  with  this  ma- 
terial, and  that  the  same  tree  grew 
on  the  banks  of  the  Amazon ;  also 
that  the  natives  made  water  tight 
boots  from  it,  which  had  the  real  ap- 
pearance of  leather,  after  having 
been  blackened  by  means  of  smoke, 
lie  goes  further  and  says  that  the  na- 
tives made  some  moulded  goods  from 
this  material.  From  his  writings  we 
find  several  of  the  terms  still  in  use. 

I  mention  this  simply  to  give  some 
idea  as  to  the  length  of  time  civ- 
ilized man  has  been  acquainted  with 
this  important  substance,  and  in  what 
condition  and  state  of  development 
he  found  it. 

In  the  beginning  it  is  well  to  de- 
fine a  few  of  the  terms  which  will  be 
used  and  describe  briefly  the  labor 
condition  which  prevails  throughout 
nearly  all  of  the  South  America  rub- 
ber regions. 

Thus  far  very  little  of  the  vast  ter- 
ritory bearing  these  rubber  produc- 
ing trees  has  been  even  explored,  to 
say  nothing  of  their  being  available 
for  tapping.  It  is  estimated  that  there 


are    at    present    300,000,000     virgin 
trees  in  this  territory. 

Tracts  of  this  rubber  producing 
region  are  obtained  by  individuals  or 
companies  on  lease  from  the  state, 
and  the  working  of  any  area  which 
has  not  been  surveyed  by  the  state  is 


FIG.  1 

punishable  under  the  law  of  theft. 
The  number  of  leases  and  sub-leases 
is  considerable.  From  the  report  of 
the  Commission  of  Economic  Expan- 
sion in  Brazil  during  the  year  1906- 
07  there  were  organized  fifty-two 
such  companies  with  a  capital  of  two 
millions  sterling.  These  concessions 
are  termed  scringals,  and  are  usually 
computed  according  to  the  number 
of  estradas  running  through  them. 
The  cxtradas  are  paths  running 


RUBBER  OF  THE  AMAZON  BASIN 


through  the  forest  in  such  a  way  as 
to  lead  past  from  one  hundred  to  one 
hundred  and  fifty  trees.  Sometimes 
the  trees  are  some  distance  apart,  but 
generally  they  are  found  in  groups  of 
from  two  to  six. 

The  seringueiro  is  the  name  applied 
to  the  one  taking  care  of  a  seringal. 
The  seringueiros  are  mostly  natives  of 
the  states  of  Ceara  and  Maranhao. 
Due  to  the  high  death  rate  and  the 
great  number  of  desertions,  it  is  nec- 
essary to  provide  about  eighty  labor- 
ers for  a  seringal  on  which  fifty  could 
actually  do  the  work.  One  serin- 
gueiro is  supposed  to  take  care  of  two 
estradas  after  they  are  opened  up  and 
put  into  operation. 

The  cost  of  financing  a  seringal  is 
rather  high,  as  Sandmann  has  esti- 
mated it  costs  about  $25,000  to  put 
into  operation  a  seringal  of  one  hun- 
dred estradas,  that  is,  from  10,000  to 
15,000  trees.  This  will  buy  the  outfit 
necessary,  cut  the  paths,  build  the 
huts  and  factory,  and  also  allow  for 
a  little  incidental  expense. 

The  patrao,  the  owner  or  sub-owner 
of  a  seringal,  very  seldom  finances  his 
own  property.  He  obtains  the  ad- 
vances from  the  large  dealers  and  ex- 
port firms  at  Para  and  Manaos.  They 
are  termed  aviadorcs.  Thus  it  will  be 
seen  that  the  financing  is  really  done 
by  the  aviadores,  and  they  hold  a 
mortgage  on  the  patrao,  who  in  turn 
mortgages  the  labor  of  the  serin- 
gueiro. 

The  average  vield  of  a  six  months' 


season  of  an  industrious  seringueiro 
is  about  eight  hundred  pounds  of 
rubber.  When  he  has  paid  his  ad- 
vances to  the  patrao  there  remains  a 
profit  of  about  $250  to  $300.  This  is 
hardly  sufficient  to  support  his  fam- 
ily at  the  seat  of  operations  during 
his  absence  on  the  seringal.  It  is  for- 
tunate for  him  that  the  streams  and 
forest  furnish  fishing  and  hunting  al- 
most sufficient  to  support  him,  but 
because  of  the  poor  way  in  which  the 
food  is  prepared  and  the  unhealthy 
climatic  conditions,  there  is  much 
sickness  and  the  mortality  is  high. 
The  occupation  of  a  seringueiro  is  not 
an  enviable  one. 

Varieties 

In  the  Amazon  Basin  we  find  the 
order  of  Euphorbiaceae,  the  most  im- 
portant genus  of  which  is  the  Hevea, 
and  here  we  find  many  different 
species,  the  most  important  one  be- 
ing the  Hevea  brasiliensis,  the  species 
from  which  the  widely  known  Para 
rubber  is  obtained.  This  species  is 
found  over  a  large  part  of  northern 
South  America  but  principally  in  the 
areas  watered  by  the  Amazon  and  its 
tributaries,  in  the  states  of  Para, 
and  Amazonas,  in  Brazil.  This  is  the 
species  from  which  the  Eastern  plan- 
tations have  been  largely  propagated. 
It  is  a  large  tree,  in  its  natural  state 
often  attaining  a  height  of  one  hun- 
dred feet  and  a  diameter  of  forty 
inches. 

There  are  several  varieties  obtained 
from  the  Hevea  brasiliensis. 


Fir..  2 — RUBBER  GATHERERS  DRESSED  FOR  A  HOLIDAY 


AVe  find  two  main  regions  in  which 
Fine  Para  is  prepared,  the  ' '  Islands  ' ' 
at  the  mouth  of  the  Amazon  River; 
and  the  "  Up-river  "  regions  near 
and  above  Manaos.  "  Islands  "  rub- 
ber is  generally  known  as  "  soft- 
cure,"  and  "  Up-river  "  as  "  hard- 
cure.  ' ' 

The  scraps  of  rubber  adhering  to 
the  bark  of  the  trees  and  coagulating 


FIG.  3 — TAPPING  WILD  RUBBER  TREES 

cups  are  compressed  into  irregular 
forms  and  sold  as  "  Negroheads." 
"  Up-river  Negroheads  "  are  gener- 
ally called  ' '  scrappy  ' '  and  ' '  Islands 
Negroheads  "  are  called  "  Sernam- 
by. "  There  is  another  variety-  of 
negrohead,  the  Cameta,  coming  from 
a  district  of  that  name  in  Southwest 
Para. 

This  same  species  supplies  from  the 
Province  of  Matto-Grosso,  in  Brazil: 
the  Matto-Grosso,  Fine  and  Entre- 
fine ;  Matto-Grosso,  Virgin  Sheets, 
and  Matto-Grosso,  Negroheads. 

From  Bolivia  we  obtain  Bolivian, 
fine,  medium  and  coarse;  also  Mol- 
lendo,  fine,  medium  and  coarse.  These 
are  also  obtained  from  a  species  of 
Hevea. 

From  Peru  we  get  Peruvian  (fine. 


coarse  or  scrappy),   likewise   of   the 
Hevea. 

From  Ecuador  we  obtain  a  new 
species,  the  Sapium,  several  varie- 
ties of  which  are :  Ecuador  scrap, 
sausage;  Esmeralda  sausage,  Caucho 
bianco,  and  Caucho  negro. 

Confused  with  these  last  two  we 
often  come  in  contact  with  a  variety 
known  as  Caucho  Balls  which  is  of 
the  Hevea  brasilicnsis. 

During  the  last  quarter  of  a  cen- 
tury large  quantities  of  Caucho  have 
been  found  in  the  districts  of  Obidos, 
Tocantins,  Xingo,  and  Tapajos  rivers. 
This  supply  is  likely  to  be  exhausted 
due  to  the  fact  that  the  natives  gather 
this  latex  by  cutting  down  the  tree 
and  then  bleeding  it. 

There  are  some  seventy  varieties  of 
the  Manihot  rubber  but  we  shall  call 
attention  to  but  two,  the  Ceara  and 
Manicoba  which  grow  in  a  relatively 
poor  soil  and  at  altitudes  where  most 
other  rubber  producing  trees  cease  to 
exist.  The  bulk  of  these  rubbers  come 
from  the  Province  of  Ceara,  Brazil. 
There  is  some  difficulty  in  collecting 
this  latex  due  to  its  rapid  coagulation. 

The  natives  allow  the  latex  to 
coagulate  as  it  flows  down  the  tree 
and  then  peel  it  from  the  bark.  It 
sometimes  runs  down  onto  the  ground 
and  is  caught  in  a  leaf  formed  as  a 
receptacle.  The  result  is  that  the 
Manicoba  rubber  varies  a  great  deal 
and  contains  a  large  amount  of  for- 
eign matter.  When  this  rubber  is 
properly  prepared,  however,  it  is  of 
a  very  good  grade. 

The  Micandras  occurs  on  the  upper 
Amazon  and  some  are  of  the  opinion 
that  it  is  used  largely  in  the  making 
of  Scrappy  Negroheads. 

A  rubber  of  the  species  Hancornia 
is  also  found  in  Brazil  and  is  sold 
under  the  name  of  Matto-Grosso 
Sheets,  Mangabeira,  or  Pernambuco. 
It  is  -of  medium  value  and  rather 
large  quantities  of  it  are  used. 

The  above  enumeration  does  not 
include  all  of  the  varieties  of  rubber 
from  South  America  but  it  does  cover 
the  most  important  ones. 

Two  Methods  of  Tapping 

All  of  the  South  American  rubber 
comes  from  trees  and  is  obtained  by  a 


RUBBER  OF  THE  AMAZON  BASIN 


system  of  tapping  of  one  kind  or 
other.  We  shall  consider  two  general 
methods. 

1.  Felling  of  trees. 

2.  Bleeding   by   puncture    or    inci- 
sion, tapping. 

liy  the  felling  process  it  is  possible 
to  obtain  only  the  latex  which  is  in 
the  tree  at  the  time  of  its  cutting. 
The  method  is  a  destructive  one  and 
is  only  practiced  now  under  two  con- 
ditions. 

The  trees  found  in  Peru,  when  once 
tapped  are  attacked  by  insects  and 
the  death  of  the  tree  results,  while  if 
this  tree  is  cut  down  there  springs  up 


FIG.  4—  SMOKIXG  CAOUTCHOUC 

from  its  stump  several  sprouts  which 
grow  very  rapidly  and  in  a  short  time 
a  clump  of  trees  exists  where  there 
was  but  one  originally.  In  the  sec- 
ond place  felling  is  allowed  where  it 
is  necessary  to  thin  out  the  forests  in 
order  to  make  the  estradas. 

Several  different  methods  of  tap- 
ping are  in  use.  The  ArrocTio 
system  was  one  of  the  first  to  be 
used  in  Brazil,  and  was  accomplished 
by  binding  a  rope  obliquely  about  the 
Hevea,  the  knot  being  high  up  on  the 
tree.  Above  the  ligature,  incisions 
were  made  with  any  sort  of  tool  the 
operator  happened  to  have,  a  butch- 
er's knife,  pruning  hook,  or  cutlass, 
and  the  seringueiro  cared  little  wheth- 


er the  incision  was  too  deep  and  thus 
impaired  the  life  of  the  tree,  and  got 
injurious  material  into  the  latex,  or 
too  shallow  and  thus  obtained  a  poor 
yield  of  latex. 

From  these  incisions  the  latex  flows 
down  the  tree  until  it  comes  to  the 
rope  and  then  on  down  the  groove 
which  the  tree  forms  with  the  rope 
until  it  reaches  the  lowest  point  where 
it  is  collected  in  a  suitable  receptacle. 
The  latex  making  this  journey  down 
the  tree  collects  moss,  wooden  debris 
and  other  impurities  and  these  are  all 


FIG.    5 — NATIVE    COLLECTING    THE    LATEX 

later  found  in  the  rubber.  In  addi- 
tion to  getting  poor  rubber  the  serin- 
gueiro would  often  neglect  to  remove 
the  rope  and  the  tree  would  die  of 
strangulation.  This  process  has  been 
practically  abandoned. 

The  present  method  of  tapping  in 
this  region  has  been  described  by  a 
great  many  different  writers.  Chapel 
and  Carrey  have  probably  given  the 
best  description.  The  seringueiro 
gets  his  outfit  all  together  which  con- 
sists of  a  machado.  a  small  hatchet 
with  a  short  handle  and  a  blade 
only  3  centimeters  wide  with  a 
sharp  cutting  edge  of  about  5  centi- 
meters, the  bucket  for  carrying  the 
latex,  and  the  tigelinhas,  small  cups 


RUBBER    MANUFACTURE 


which  are  hung  at  the  different  in- 
cisions. 

With  this  equipment  the  serin- 
gueiro  starts  out  about  five  o'clock  in 
the  morning  to  operate  on  his  es- 
trada,  which  begins  at  his  hut  and 
after  its  ramifications  leads  back  to  his 
hut  again.  He  takes  with  him  his  ma- 
chado  and  tigelinhas.  When  he  comes 
to  a  tree  he  cleans  away  the  rubbish 
at  its  foot,  cleans  the  bark,  and  then 
begins  to  tap  the  tree.  With  a 
single  cut  of  the  machado  he  incises 
the  bark,  so  that  the  latex  flows  out, 
being  careful  not  to  wound  the  tree. 
After  several  incisions  of  this  kind 
have  been  made  in  each  tree,  he  places 
a  tigelinhas  under  each  one  to  collect 
the  latex  and  then  moves  on  and 
repeats  the  operation  on  the  next  tree. 

Some  of  the  collectors  make  V- 
shaped  incisions  and  others  make  ver- 
tical ones.  Whichever  method  is  used 
should  be  practiced  regularly  on  the 
tree  for  it  has  been  found  that  by 
using  irregular  tappings  the  tree  will 
yield  regularly  only  for  a  year  or  two 
and  will  then  dry  up  and  cease  to 
give  any  latex. 

A  seringueiro  is  able  to  operate 
about  fifty  trees  a  day  so  if  his 
estrada  contains  one  hundred  and 
fifty  trees  he  divides  it  in  such  a  way 
that  each  tree  is  tapped  every  third 
day.  If  his  estrada  contains  one  hun- 
dred, then  each  tree  is  tapped  every 
other  day.  After  he  has  tapped  his 
fifty  trees  he  comes  into  his  hut  for  a 
little  rest  and  a  cup  of  coffee. 

This  has  consumed  about  three  hours 
and  he  now  takes  up  his  balde,  or  tin 
bucket,  and  revisits  the  trees  which 
he  has  tapped,  pouring  the  latex  from 
each  tigelinhas  into  his  gathering 
bucket  and  turning  the  tigelinhas  up- 
side down  on  a  stick  near  the  foot  of 
the  tree.  This  is  done  to  prevent  its 
being  filled  with  water  and  collecting 
impurities,  as  it  rains  every  day  dur- 
ing this  season  of  the  year. 

The  period  of  collecting  latex  is 
from  the  later  part  of  August  to  the 
first  of  January.  After  all  of  the 
latex  is  gathered  he  returns  to  his  hut 
and  the  remainder  of  the  day  is  spent 
preparing  the  rubber  from  this  run. 

Latex  is  the  liquid  containing  the 


rubber  which  exudes  from  the  tree, 
but  is  not  the  sap  of  the  tree.  It  may 
be  thought  of  as  analogous  to  the  milk 
of  mammals,  which  it  is  often  called, 
the  rubber  corresponding  to  the  but- 
ter fat,  and  of  course  must  be  sep- 
arated out.  The  process  of  obtaining 
the  rubber  from  the  latex  is  called 
coagulation. 

Coagulating  Latex 

The  workman  starts  a  fire  in  his 
fumiero,  a  kind  of  furnace  sur- 
mounted by  a  short  conical  pipe 
which  will  deliver  the  fumes  so  that 
they  do  not  spread  too  far  afield.  He 
then  fills  his  fumicro-  with  the  fuel 
which  has  been  carefully  selected  and 
ignites  it.  The  best  fuel  for  this  pur- 
pose is  the  nuts  of  the  urucuri.  Some 
wood  is  mixed  with  these  to  keep 
them  burning,  and  also  to  conserve 
the  supply. 

As  soon  as  the  smoke  is  given  off 
abundantly  the  cauchero  takes  a 
paddle  and  holds  this  in  the  smoke 
from  his  fumiero  until  it  is  covered 
with  a  layer  of  carbon.  This  is  done 
to  prevent  the  rubber  from  sticking 
to  it.  He  then  dips  the  paddle  into 
the  latex  at  his  side,  allows  it  to  drain, 
then  holds  it  in  the  dense  smoke  until 
it  assumes  a  yellow  tinge. 

The  rubber  is  coagulated  almost 
immediately  and  the  mother  liquor 
exudes  and  is  evaporated  by  the  heat 
of  the  fumiero.  When  this  is  done, 
the  first  layer  is  complete  and  he 
again  dips  the  paddle  into  the  latex 
and  repeats  the  same  process,  thus 
building  up  a  biscuit  of  rubber  with 
one  thin  layer  upon  another  and  each 
one  coagulated  separately. 

When  this  biscuit  has  attained  » 
weight  of  ten  or  eleven  pounds  he 
frees  it  from  the  paddle  by  cutting  it 
down  in  the  direction  of  its  axis  and 
is  now  ready  to  begin  over.  These 
biscuits  are  still  moist  and  to  dry 
them,  he  places  them  in  the  sun  for 
several  days.  They  are  then  ready 
for  the  market  under  the  name  of 
Para  Fine.  The  size  and  shape  of 
these  biscuits  varies  considerably  in 
accordance  with  the  way  they  are 
made. 


RUBBER  OF  THE  AMAZON  BASIN 


FIG.  G — MKTIIOD  OF  SMOKING  RUBBER 


this  over  his  fire  by  placing  one  end 
in  a  loop  suspended  from  the  roof  of 
his  hut  and  holds  the  other  end  in  his 
left  hand,  with  which  he  keeps  it 
turning  continually,  while  with  the 
other  hand  he  pours  a  small  amount 
of  latex  over  the  pole  which  is  in  the 
smoke.  By  this  method  the  same 
grade  of  rubber  is  produced  but  in 
larger  biscuits,  averaging  about  forty 
or  fifty  pounds.  This  is  the  method 
of  coagulating  the  latex  of  all  of  the 
Paras,  and  it  is  undoubtedly  the  vir- 
tues of  this  process  which  has  given 
the  Para  its  enviable  position  in  the 
rubber  trad*-. 

There  are  two  reasons  at  least  for 
the  excellence  of  this  rubber :  first,  the 
smoke  lias  a  large  amount  of  carbon  in 
it  and  we  know  this  substance  pos- 
sesses energetic  antiseptic  properties; 
second,  in  the  products  of  distillation 
of  the  uricnri  nuts  there  is  a  consider- 
able amount  of  creosote  which  also 
possesses  the  same  property.  There- 
fore we  have  a  double  protection 
against  fermentation  and  decomposi- 
tion of  the  nitrogenous  matter  present 
in  rubber  coagulated  by  this  method. 

The  Manihot  latex  is  coagulated  by 
natural  heat.  As  was  stated  before, 
the  s< .rin(/ii<  iro  obtains  the  Ceara  and 
Manitoba  by  tapping  the  tree  with 
long  gashes  as  high  up  on  the  tree  as 


he  can  reach.  The  latex  is  very  thick 
and  coagulates 
before  it  ever 
comes  to  the 
ground.  H  e 
allows  it  to  re- 
main two  o  r 
three  days  or 
until  it  is  dry, 
when  he  de- 
taches it  a  n  d 
either  rolls  it 
up  into  a  ball 
o  r  folds  i  t 
back  and  forth 
u  p  on  itself. 
Without  f  u  r  - 
ther  treatment 
it  comes  into 
the  market  as 
Ceara  Scraps, 
There  are 
three  grades 
of  this  rub- 
.  her ;  the  first 
quality  is  a 
blonde  rubber 
which  is  collected  at  the  beginning 
of  the  season ;  the  second  quality  is 
darker  in  color,  and  is  collected 
later  on  when  the  rains  have  begun 
to  fall ;  the  third  quality  is  that 
which  is  collected  at  the  foot  of  the 
trees  and  is  full  of  earthy  mate- 
rial, often  as  much  as  50  per  cent. 


FIG.  7 — BALL  OF  RUB- 
BKR  AFTER   SMOKING 


10 


RUBBER    MANUFACTURE 


This  rubber  always  gives  off  a 
strong  smell  due  to  the  careless  treat- 
ment in  its  collection.  Naturally  this 
is  a  higher  grade  latex  than  that  from 
the  Hevca,  and  it  is  a  pity  that  more 
care  is  not  exercised  in  its  prepara- 
tion. 

A  chemical  means  of  coagulation 
was  proposed  by  Strauss  for  use  with 
the  Hancornia  latex.  It  consists  in 
pouring  into  the  latex  a  solution  of 
potassium  alum  when  coagulation 
takes  place  immediately.  The  rubber 
is  then  allowed  to  drain  for  about 
eight  days,  then  divided  into  small 
pieces  and  sun-dried  for  a  month 
when  it  is  ready  for  market. 

Due  to  the  rapid  coagulation,  we 
find  enclosed  latex  all  through  rubber 
made  by  this  process  which  not  only 
constitutes  loss  but  which  further  fer- 
ments and  produces  a  bad  odor;  we 
also  find  pockets  filled  with  the  alum 
solution  which  has  a  very  injurious 
effect  upon  the  rubber.  As  a  result 
this  rubber  deteriorates  with  age,  and 
it  often  has  a  loss  of  as  high  as  60  per 
cent.  There  are  three  grades  of  Man- 
gabeira,  and  the  one  possessing  a 
red  color  sells  at  a  premium. 

This  alum  process  has  been  dis- 
placed in  certain  regions  by  sulphuric 
acid,  but  this  does  not  remedy  the 
objections  already  mentioned,  and  of 
course  it  has  no  antiseptic  property. 
To  correct  this,  a  solution  of  common 
salt  has  been  used  but  it  leaves  too 
large  a  quantity  of  water  in  the  rub- 
ber. A  soap  solution  has  been  used 
but  this,  in  addition  to  having  the 
same  objections,  acts  very  slowly. 

The  juices  of  some  plants  and 
climbers  have  also  been  employed,  but 
the  difficulty  of  obtaining  these  and 
the  fact  that  they  introduce  more 
resins  into  the  rubber  has  resulted  in 
their  condemnation. 

The  above  comprise  the  more  im- 
portant methods  of  coagulation  which 
are  in  use  or  have  been  used  in  South 
America,  the  best  one  being  the 
smoking,  and  it  is  worthy  of  mention 
in  this  connection  that  this  is  the 
method  which  de  La  Condamine 
found  the  natives  using  in  1731. 


One  thing  which  consumers  of  rub- 
ber are  very  anxious  to  have  is  uni- 
formity, and  there  are  several  factors 
which  tend  to  produce  a  poor  prod- 
uct: 

First,  if  the  trees  have  been  im- 
properly tapped,  that  is  if  the 
seringueiro  has  cut  too  deeply  and 
pierced  the  cambium,  some  of  the  sap 
of  the  tree  will  enter  the  latex  and 
impair  the  rubber,  making  it  tacky; 

Second,  when  in  gathering  the 
latex  of  one  species  is  mixed  with 
that  of  another  or  even  with  that  of 
a  tree  that  is  too  young ; 

Third,  carelessness  in  gathering 
and  coagulating.  The  most  uniform 
varieties  therefore  are  the  Hevea  and 
Manihot. 

The  following  table  gives  some  idea 
of  the  relative  loss  in  washing: 

Fine  Para  (hard  or  soft)...  12  to  20  percent 

Negroheads    20  to  40  per  cent 

Manicoba    28  to  30  per  cent 

Matto   Grosso 15  to  30  per  cent 

Mangabeiro    30  to  35  per  cent 

To  give  some  notion  as  to  the 
progress  made  in  the  production  of 
rubber  from  South  America,  the  fol- 
lowing facts  are  interesting: 

In  1825,  less  than  30  tons  of  rubber 
were  exported;  in  1830  there  were 
156  tons;  in  1840,  388  tons;  in  1850. 
1,467  tons;  in  1860,  2,670  tons;  and 
in  1897,  Brazil  alone  produced  21,260 
tons. 

From  1909  to  1913,  the  yearly  aver- 
age was  between  39,000  'and  '  40,000 
tons.  The  May,  1917,  issue  of  the 
"  World's  Rubber  Position  "  gives 
the  following  estimate  of  the  world's 
production  of  rubber  in  1916 : 

Plantation    152,650  tons 

Brazilian    .•'.r>.500  tons 

Other   sources 12,448  tons 

To  show  the  ratio  of  plantation  to 
Brazilian  for  several  years  the  follow- 
ing data  are  significant : 

Plantation        Wild  Rubbers 

Tons  Tons 

1910 8.200  40.800 

1011 ]  4.41  li  39.730 

1012 2S,51S  42.410' 

1913 47.01  ^  39.370 

1914 71..'!^"  ::7.000 

1915 107.807  37,220 

1916 152.0.->n  36.500 

1917 223.000  52.62S 

191S. 188.00H  40.629 

1919 358.000  41.635 


CHAPTER  III 
African  Rubbers,  Including  Those  from  Madagascar 


f  arieties 

The  larger  part  of  the  African  rub- 
ber trees  are  oi  the  order  Apocyna- 
ceae,  of  which  there  are  many  gen- 
erae  but  three  of  these  produce  the 
majority  of  the  rubber.  These  are 
Flint  iiniia,  Landolpliia,  and  Clitan- 
dra.  The  rubbers  are  all  more  adhe- 
sive but  less  elastic  than  Para. 

Of  the  Funtiimia  just  one  species 
is  regarded  as  of  commercial  value 
and  that  is  the  Flint umia  elastica. 
The  gums  from  the  other  species  seem 
to  be  very  resinous  and  the  natives 
are  thought  to  use  some  of  these  to 
adulterate  the  better  gums. 

The  rubber  from  Flint  it  in  ia  clastic'i 
when  freshly  coagulated  has  a  pecu- 
liar sheen  to  the  cut  surface  and  for 
that  reason  is  sometimes  called 
"  Lagos  silk  rubber."  The  main 
varieties  of  this  rubber  are  what  ap- 


pear  in  the  trade  under  the  names  of 
Gold  Coast  Lump,  Ivory  Coast  Lump, 
Niger  Niggers,  Benin  Lump,  and  some 
Congo  and  Cameroon. 

The  tree  grows  best  in  the  province 
of  Uganda  and  the  tropical  regions 
of  Africa.  The  tree  often  attains  con- 
siderable proportions,  in  fact  trees 
have  been  found  having  a  circumfer- 
ence of  eighty  inches  and  a  height  of 
one  hundred  feet,  a  tree  as  large  as 
the  Hevea. 

This  rubber  is  now  being  obtained 
on  the  plantation  scale  by  several  com- 
panies in  Uganda.  As  a  plantation 


"""""/  *  I " .  V-"°2M^^^^Tr^/j 


FIG.  7 — TAPPING  FUNTUMIA  TREE 


11 


proposition  it  has  three  advantages 
over  Hevea.  First,  it  grows  more 
rapidly;  second,  it  yields  a  larger 
amount  of  latex  for  a  small  number  of 
tappings ;  third,  it  is  able  to  withstand 
a  comparatively  long  drought. 

The  trees  recover  rather  slowly 
from  the  wound  made  by  tapping, 
however.  Another  great  objection  is 
the  fact  that  the  tree  has  so  many 
branches.  If  planted  only  a  few  feet 


12 


RUBBER   MANUFACTURE 


apart  it  will  branch  down  into  the 
lower  regions  of  the  trunk  thus  pro- 
ducing a  dense  bushy  mass.  A  tree 
standing  alone  branches  from  the 
ground  to  the  very  top.  Of  course 
these  branches  interfere  with  tapping 
and  it  is  found  that  when  they  are 
removed  by  pruning  they  heal  very 
slowly  and  show  bad  scars  for  a  long 
time. 

Dr.  Christy  suggested  the  planting 
of  these  trees  very  closely  together 
and  then  thinning  out  later.  This  has 
helped  considerably. 

The  tapping  of  the  Funtumia  is 
done  only  two  or  three  times  a  year, 
but  it  is  tapped  from  the  ground  up 
to  the  first  branches,  generally  a  dis- 
tance of  fifteen  to  eighteen  feet. 

The  tapping  is  of  the  herring-bone 
type  but  must  be  done  very  carefully 
and  must  also  be  very  shallow.  Dr. 
Christy  also  suggested  that  a  channel 
be  cut  in  the  bark  just  deep  enough 
to  carry  the  latex  and  that  the  flow  be 
started  by  means  of  a  pricker. 

This  method  gives  about  twice  as 
much  latex  as  the  Schulz-im-Hofe 
method,  which  consists  of  vertical  in- 
cisions about  four  inches  apart  and 
extending  from  the  ground  up  to  ihe 
branches.  It  has  also  been  found  that 
if  the  pricking  be  done  slowly,  by 
beginning  at  the  bottom  of  the  chan- 
nel and  taking  several  days  to  com- 
plete the  real  operation  of  tapping, 
that  a  better  grade  of  latex  is  obtained 
and  also  a  better  yield. 

This  rubber  was  first  thought  to 
be  one  of  the  species  Kickxia  and  from 
the  Kew  Bulletin  of  1890  we  notice 
the  following  statement: 

"  Tn  September.  Kew  received  from 
Captain  Denton,  C.M.G..  two  pieces  of 
the  trunk  of  Ihe  Lagos  rubber  tree,  each 
about  ten  inches  to  a  foot  in  diameter, 
scarred  with  the  marks  of  the  rubber 
gatherers.  They  were  sent  as  the  'female' 
rubber  tree,  a  name,  we  learn,  that  is 
locally  applied  to  the  Kick.ria  africann. 
Benth.  It  is  thus  distinguished  from 
TfolarrJiciiu  afrirana,  quite  a  different 
plant,  which  is  fancifully  called  the  'male' 
rubber  tree.  The  later  is  also  an  ^/)oe?;- 
naceoua  plant,  but  not  known  to  yield  any 
rubber. 

"  Should  the  new  rubber  Kick-ria  con- 
tinue of  commercial  value,  there  is  no 
doubt  that  it  will  eventually  be  possible 
to  establish  plantations,  and  thus  make 
the  industry  a  permanent  one.  It  has 


always  been  seen  that,  owing  to  the  climb- 
ing habit  of  the  Landolphia.  which  have 
hitherto  yielded  African  rubber,  it  was 
not  practicable  to  cultivate  them  in  regular 


FIG.   9 — SWAHILI  CLIMBING  METHOD 

plantations,  as  they  require  the  support 
of  other  plants,  and  when  once  tapped, 
many  years  should  have  to  elapse  before 
they  would  be  fit  to  yield  another  crop. 
With  the  Kickifia  these  practical  diffi- 
culties disappear.  According  to  Chalot. 
Kickxia  africana,  has  been  lately  found 
in  Gaboon.  Specimens  have  been  meas- 
ured which  were  one  meter  in  circum- 
ference and  twelve  to  fifteen  meters  high. 
Each  tree  is  estimated  to  yield  annually 
\vithout  any  injury." 

Wright  however,  in  his  Cantor 
Lectures,  1907,  points  out  the  error 
of  the  Kew  observations,  for  he  says : 

"  Fitntinnid.  This  genus  has  lately  be- 
come known  as  a  source  of  rubber  in 
Africa.  It  is  still  much  confused  with 
the  genus  Kick  x  In,  and  it  is  as  well 
to  again  point  out  that  Africa  does  not 
possess  a  single  species  of  Kickxia  of 
value  as  a  rubber  producing  plant.  The 
four  species  of  Kick.ria  acknowledged  by 
Stapf.  are  found  only  in  Java.  Celebes, 
Philippine  Islands,  and  Borneo. 

"The  genus  Fitnlinnni  is  partly  African 
;ind  is  represented  by  three  species.  /•'. 
rlast lea,  Stapf..  F.  africana,  Stapf.,  and 
F.  latiffilin,  Stapf.-  The  species  of  im- 
portance in  Africa  is  F.  cliixiica,  Stapf. 
Its  occurrence  has  been  recorded  in 
Liberia.  Gold  Coast.  Ashanti.  Lower 
Nigeria.  Cameroons.  Mnndame.  French 
Congo.  Congo  Free  Slates.  Uganda. 

"The  rubber  from  this  species  is  very 
valuable,  possessing  when  properly  pre- 
pared from  eiiihty  to  ninety  per  cent  of 


AFRICAN  RUBBERS,  INCLUDING  THOSE  FROM  MADAGASCAR 


13 


Fro;   1.0 — TAPPING  A  Ri  IMSF.I:  VINK 

caoutchouc.  I'' it  n  I  ii  in  id  cluxtiru  II.MS  been 
described  :is  ;i  tree  with  :i  cylindrical 
trunk  which  attains  a  height  of  one  hun- 
dred feet ;  sometimes  the  tree  occurs  more 
ahiiiidantl.v  in  local  areas,  and  out  of  an 
area  of  about  fifty-four  square  miles  as 
many  as  one  million  seven  hundred  and 
sixty  lives  have  bec>n  estimated  to  oc- 
cur." 

The  Manihot  Gluziovii  has  been  in- 
troduced into  British  Central  Africa. 
In  regard  to  the  advisability  of  this 
project  \vc  find  a  diversity  of  opinion. 
some  thinking  it  will  prove  a  fine 
plantation  species  and  others  raising 
great  objections  to  it. 

Before  taking  up  the  Landolphias  it 
is  necessary  to  define  some  of  the 
terms  which  will  be  used  in  describ- 
ing these  rubbers. 

BALI,:  The  most  common  form  of 
rubber  coming  from  Africa.  These 
halls  vary  in  si/.e  from  an  inch  or  less, 
known  as  ''  Small  ball."  up  to  four 
inches  or  more  in  diameter,  and 
known  as  "  Large  ball." 

THIMBLES:  The  natives  make  these 
by  cutting  the  rubber  up  into  small 
cubes,  which  are  sometimes  called 
"  Nuts,"  as  for  example  "  Ambri/ 
nuts." 

LUMP  :  A  very  common  form  of 
these  rubbers  consisting  simply  of 
large  irregular  pieces  which  often  be- 
come stuck  together  in  transportation. 


FLAKE:  A  form  of  lump  which  is 
very  soft  and  is  used  in  frictions. 

PASTE:  Practically  the  same  as 
flake. 

STRIPS:  Made  from  lump  rubber 
by  cutting  and  pressing  before  it  is 
sold. 

BUTTONS  are  made  in  the  same 
manner  as  strips  with  the  exception 
that  they  are  in  small  pieces. 

BISCUITS  and  OYSTERS:  The  same 
as  buttons. 

NIGGERS  and  TWIST  rubbers :  A 
Form  of  ball. 

The  Landolphias  are  all  creepers  or 
vines,  yet  attain  considerable  size. 
Often  vines  are  found  having  a  diam- 
ter  of  six  inches.  There  are  several 
species  of  importance,  the  Landolphia 
Owaricnsis,  Landolphia  Hendelotii, 
Landolphia  Thollonii,  Landolphia 
Sphacrocarpa,  and  the  Landolphia 
Picrrci.  The  last  two  are  found 
largely  in  Madagascar. 

The  rubbers  from  this  species  re- 
ferred to  in  the  trade  are,  Red 
and  Black  Kassai  from  the  Congo 
region  ;  Upper  Congo  balls  and  Equa- 
teur  also  from  the  Congo  region ; 
Virgin  Sheets  and  Pinky  from  Mada- 
gascar; Sierra  Leone  Niggers,  Twists, 
and  Cake  all  coming  from  the  Sierra 
Leone  and  southern  rivers;  Conakry 
Niggers,  Soudan  Niggers  and  Twists, 
coming  from  French  ^^Test  Africa ;  the 
Bassam  Niggers  and  Twists  likewise 
the  Lab ou  Niggers  come  from  the 
same  territory ;  Liberia  Lump,  Hard 
Flake  and  Soft  produced  in  the 
Sierra  Leone  district;  Accra  found 
on  the  Gold  Coast  and  coming  into 
the  market  graded  as  "Prime," 
"Seconds,"  "Thirds"  and  lower 
grades  of  "Flake  and  Paste": 
Gaboon,  probably  the  best  known 
Flake;  Lapori,  a  Congo  rubber  and 
represented  by  Balls,  Strips,  and 
Cakes,  some  of  the  Balls  being  very 
clean  and  good.  From  Angola  we  ob- 
tain Loan  da.  Thimbles.  Niggers,  and 
Prima.  also  Angola  Niggers.  There 
are  several  grades  coming  from  the 
port  of  Mozambique  in  the  form  of 
Marbles.  Balls,  Spindles,  and 
Sausage. 

The  Clitandra  are  widely  distrib- 
uted throughout  Africa.  They,  too, 


14 


RUBBER    MANUFACTURE 


are  vines  and  flourish  in  great  num- 
bers on  the  Gold  Coast  and  the 
Congo.  Their  rubber  comes  into  the 
market  largely  as  Lower  Congo  in  the 
form  of  small  cubes. 

In  the  above  we  have  not  mentioned 
all  of  the  varieties  of  rubber  which 
Africa  furnishes  but  we  have  tried  to 
call  attention  to  the  representative 
classes  of  rubber  now  in  use. 

Coagulation 

Concerning  the  coagulation  of  these 
African  rubbers  not  a  great  deal  is 
known,  in  fact  we  do  not  know  how 
some  of  them  are  obtained  by  the  na- 
tives. Therefore  we  shall  describe 
methods  in  use  with  the  different 
genera  ralher  than  with  the  different 
species. 

The  latex  from  the  Funtumia  is 
coagulated  by  boiling  and  this  is  the 
method  employed  by  the  natives. 
They  sometimes  use  a  fusion  from  the 
leaves  of  Banhinia  reticulate  to  facili- 
tate the  coagulation  by  heat.  This 
rubber  when  properly  prepared  is  of 
a  high  grade  and  possesses  great 
strength ;  for  that  reason  we  have  the 
methods  used  upon  the  plantations. 
From  the  Kew  Bulletin  we  get  an  idea 
of  the  two  most  general  ways : 

"  There  are  at  present  two  kinds, 
namely,  '  the  cold  process '  and  '  the  heat 
process.'  The  cold  process  is  chiefly  prac- 
tised by  the  Fanti  men  introduced  from 
the  Gold  Coast.  A  cavity  is  excavated 


in  the  trunk  of  a  fallen  tree  so  as  to 
form  a  cistern  of  the  capacity  necessary 
for  holding  the  milk  collected  during 
several  days.  Into  this  the  rubber  gath- 
erers pour  the  milk,  after  straining  it, 
from  day  to  day  until  it  is  quite  full. 
It  is  then  covered  with  palm  leaves  and 
left  for  twelve  to  fourteen  days,  and 
sometimes  much  longer,  depending  on  the 
season,  until  most  of  the  watery  portions 
have  either  evaporated  or  sunk  into  the 
wood. 

'•  After  being  kneaded  and  pressed  to- 
gether, the  rubber  thus  obtained  has  a 
dark  brownish  color,  with  the  inner  por- 
tions of  a  slightly  lighter  color.  Such 
rubber  is  known  locally  as  '  silk  rubber.' 

"  The  heat  process  is  the  one  generally 
adopted  by  the  natives  of  Lagos.  This  is 
much  simpler  in  working,  as  it  disposes 
of  all  the  milk  collected  at  the  close  of 
each  day.  After  being  strained  the  milk 
is  placed  in  a  vessel  and  boiled.  The 
rubber  begins  to  coagulate  almost  di- 
rectly the  heat  is  applied  and  after  the 
boiling  is  over  is  removed  in  a  somewhat 
sticky  condition  owing  to  being  burnt, 
and  of  a  blackish  color. 

"  It  is  pointed  out  that  the  heat  pro- 
cess, though  simpler,  impairs  the  quality 
of  the  rubber,  and  is  calculated  to  injure 
the  industry.  It  is  probable  that  if  the 
heat  process  were  somewhat  modified  the 
results  would  not  be  so  injurious. 

"An  experiment  was  tried  at  the  I.o 
tanic  station  to  coagulate  the  milk  by 
heat,  but  not  applied  directly  to  it.  The 
result  was  much  more  satisfactory.  The 
rubber  came  off  a  milky  white  color,  and 
after  being  pressed  it  was  clean  and  firm 
without  being  sticky. 

"  The  history  of  this  new  rubber  in- 
dustry in  Lagos  is  full  of  interest,  and 
illustrates  the  wonderfully  rich  resources 
in  the  vast  forests  of  West  Africa.  It 


FIG.  11 — ro,\r,rr.ATiox  OF  LATEX  AXD  PREPARING  SHEET? 


AFRICAN  RUBBERS.  INCLUDING  THOSE  FROM  MADAGASCAR 


15 


shows  also  very  clearly  how  largely  these 
resources  can  be  developed  by  judicious 
and  intelligent  action  on  the  part  of  the 
government." 

Obtaining  mitl  Coagulating  Latex  from  V  ines 

The  methods  used  by  the  natives 
for  coagulating  the  latex  from  vines 
are  very  diverse.  The  following 
methods  are  therefore  used  on  both 
the  Landolphias  and  the  Clitandras: 

it  is  said  that  the  Red  Kassai  is 
obtained  by  smearing  the  latex  over 
the  body  and  the  natural  heat  evapor- 
ating the  water  the  rubber  is  stripped 
off.  The  eollecvor  after  tapping  the 
vine  collects  the  latex  in  his  hands 
and  smears  it  over  his  body,  then  pro- 
ceeds to  his  hut  where  he  removes  the 
rubber  in  little  bits  and  makes  them 
into  balls.  Sometimes  after  tapping 
the  hand  is  placed  against  the  incision 
and  the  latex  flows  down  the  arm  and 
after  coagulation  this  is  stripped  off 
like  a  glove.  By  either  one  of  those 
methods  the  earthy  matter  is  absent 
but  is  not  absent  from  the  rubbers 
putrescible  matter. 

The  Black  Kassai  is  obtained  by  a 
process  of  boiling  and  smoking. 

The  "  Ball  "  rubbers  are  obtained 
by  bruising  the  vine.  In  some  locali- 
ties as  the  latex  exudes,  some  salt  solu- 


tion is  poured  over  it  by  means  of  a 
shell.  This  coagulates  the  latex  and  a 
little  lump  of  rubber  is  drawn  off, 
and  by  keeping  the  bruised  place 
moistened  with  the  brine  the  rubber 
is  drawn  into  a  thread  which  is  wound 
around  and  around  the  original  lump 
as  a  nucleus. 

Very  often  the  natives  will  start 
five  or  six  such  places  and  then  re- 
treat a  few  steps  and  wind  all  of 
these  threads  into  one  ball  of  con- 
venient size  to  hold  in  the  hands. 
They  make  large  balls  of  rubber  in 
this  same  manner  by  taking  the  ball 
when  it  has  become  too  large  to  wind 
in  the  hands,  and  lying  on  their 
backs,  supporting  it  on  the  stomach 
and  continuing  to  wind  it  with  the 
hands.  The  salt  solution  as  we 
know  is  a  good  antiseptic  and  there- 
fore this  rubber  does  not  as  a  rule 
develop  foul  odors,  but  it  does  con- 
tain large  amounts  of  occluded  water 
and  brine  which  are  objectionable. 

Perhaps  the  most  common  way  of 
obtaining  the  latex  from  vines  con- 
sists in  cutting  them  down  and  bleed- 
ing or  allowing  the  vine  to  dry  out 
and  then  removing  the  rubber  by  a 
process  of  maceration. 

The    method    mentioned    above    of 


FIG.  12 — DRYING  THE  SHEETS  OF  RUBBER 


16 


RUBBER    MANUFACTURE 


cutting  down  the  vinos  and  creepers 
which  produce  rubber  and  then  bleed- 
ing them  is  very  wasteful  for  a  large 
part  always  remains  in  the  wood.  To 
overcome  this  the  Madagascar  Rub- 
ber Company,  Ltd.,  has  put  into  op- 
eration the  following  method : 

They  cut  down  the  vines  and 
creepers  and  allow  them  to  dry  when 
the  rubber  which  they  contain  rapidly 
coagulates.  The  dried  material  is  now 
fed  into  a  machine  which  grinds  it  to 
a  pulp  in  the  presence  of  water. 
After  leaving  this  machine  it  goes 
through  several  machines  called 
"  agglomerators  "  which  bring  the 
particles  of  rubber  together  and  at 
the  same  time  wash  away  the  wood 
fibers.  This  process  has  effected  quite 
a  saving  in  rubber. 

Another  method  of  coagulation  by 
natural  heat  employed  by  the  natives 
consists  in  tapping,  after  cleaning 
away  the  debris  from  the  ground. 
They  then  allow  the  latex  to  collect  in 
the  sand .  which  removes  part  of  the 
water  by  filtration,  the  remainder 
being  evaporated  by  the  heat  of  the 
sun.  The  native  returns  later  and 
gathers  up  the  lump  of  rubber  with 
all  the  foreign  matter  which  adheres 
to  it  and  then  delivers  it  to  the  buyer. 
This  method  is  very  much  preferred 


by  the  natives  for  it  requires  about 
the  least  amount  of  labor  of  any 
method  known  to  them. 

The  rubber  obtained  by  this  care- 
less method  not  only  contains  the  for- 
eign matter  which  it  naturally  picks 
up  and  which  the  native  purposely 
adds,  but  also  pockets  of  occluded 
latex  containing  nitrogenous  matter 
which  putrefies  and  not  only  injures 
the  rubber,  but  gives  it  a  nauseous 
smell.  This  method  is  used  largely  in 
West  Africa  and  to  some  extent  in  the 
Congo  and  Angola. 

A  method  also  used  in  the  Congo 
consists  in  tapping  the  vine  in  several 
places,  one  below  the  other.  At 
the  lowest  one  the  native  fixes  a  leaf 
in  the  form  of  a  trough  which  will 
conduct  the  thin  stream  of  latex  out 
into  a  collecting  receptacle.  The  leaf 
is  generally  made  secure  either  by 
means  of  clay  or  partly  coagulated 
rubber.  The  collecting  receptacle  has 
a  hole  in  the  bottom  which  is  care- 
fully corked  up.  When  the  latex  has 
ceased  to  flow  there  is  added  to  it 
four  or  five  times  its  volume  of  water 
and  it  is  allowed  to  stand.  The  rub- 
ber then  comes  to  the  top  in  the  form 
of  a  semi-solid  cream. 

The  native  then  removes  the  cork 
from  the  orifice  in  the  bottom  of  the 


FIG.  13 — PREPARING  OF  FUNTUMIA  .RUBBER 


AFRICAN  RUBBERS.  INCLUDING  THOSE  FROM  MADAGASCAR 


17 


container  and  draws  off  the  lower 
liquid.  This  contains  the  majority 
of  the  putrescible  matter.  The  rub- 
ber is  then  removed  to  wooden  con- 
tainers where  it  is  exposed  to  the  air 
for  some  time,  depending  upon  its 
condition.  The  native  judges  from  its 
appearance  when  it  is  ready  for 
kneading.  If  it  gets  too  hard  for  this 
it  is  cut  up  into  small  parts  and  is  sold 
as  "  thimbles." 

This  method  is  open  to  the  same 
criticism  as  the  others;  namely,  the 
putrescible  matter  is  enclosed  in 
pockets  wher"  it  decomposes  and  pro- 
duces a  sickening  smell. 

The  process  of  using  potassium 
alum  is  in  vogue  in  Africa  in  just 
about  the  same  manner  as  in  South 
America. 

Citric  acid  has  been  used  with  the 
iatex  from  the  Landolphias  but  it  has 
been  completely  replaced  by  sulphuric 
acid  in  Madagascar.  Lime  juice  has 
also  been  used  in  a  few  localities. 
These  all  have  the  same  objection 
that  they  coagulate  too  rapidly  and 
thus  enclose  some  of  the  latex. 

The  properties  of  these  African 
rubbers  may  be  summarized  as  fol- 
lows: Gold  Coast  Lump,  from  which 
Si  rips  and  Buttons  are  made,  is  a 
very  good  grade  of  rubber.  The 
Flake,  however,  is  generally  wet  and 
has  a  bad  odor.  Ivory  Coast  is  also 
a  good  rubber.  Niger  Niggers  at 
first  were  very  poor,  suffering  a  loss 
as  high  as  forty  to  fifty  per  cent  upon 
washing,  but  they  are  coming  into  bet- 
:»-r  repute  at  present. 

Benin  is  generally  very  dirty  and 
has  a  very  bad  smell.  Congo  con- 


tains bark  and  water,  likewise  pock- 
eted latex.  The  Red  Kassai  is  the 
best  rubber  from  Congo  possessing  a 
high  tensile  strength.  The  black  is 
not  as  good  and  does  not  come  as 
clean. 

The  Sierra  Leone  comes  in  several 
grades  containing  bark  and  grit  but 
low  in  moisture.  Equateur  is  a  much 
esteemed  rubber.  Bassam  Niggers  if 
in  the  form  of  small  balls  are  good. 
Lahou  Niggers  are  about  the  same. 
Liberia  is  wet  and  a  more  or  less  pasty 
rubber.  Accra  varieties  are  of  a  fair 
rank. 

Gaboon  is  coagulated  by  an  un- 
known process.  It  is  very  bulky  but 
will  take  the  form  of  the  container 
in  which  it  is  shipped.  It  runs  very 
high  in  moisture.  The  Lapori  is  a 
variable  rubber  as  some  of  it  runs  in 
good  clean  condition  and  some  con- 
tains fermented  milk. 

The  Loanda  is  gradually  disappear- 
ing and  its  place  is  taken  by  Angola 
Niggerheads.  The  Mozambique  rub- 
bers are  sold  largely  in  the  Liverpool 
market  where  they  are  in  demand. 
The  Pinky  from  Madagascar  is  a  very 
good  rubber,  but,  due  to  the  reckless 
methods  of  obtaining  it,  is  liable  to 
become  extinct. 

From  the  following  table  showing 
the  loss  in  washing  one  may  obtain 
an  idea  of  the  relative  values  of  these 
African  rubbers. 

Red  and  Black  Kassai  and  Equateur,  6 
to  12  per  cent:  African  Niggers  (Sou- 
dan. Conakry.  Sierra  Leona.  Niger).  15 
to  40  per  cent :  Madagascar  Pinky,  IS  to 
20  per  cent;  Madagascar  Niggers.  40  to 
50  per  cent. 


CHAPTER  IV 


Central  American  Rubbers 


When  we  refer  to  the  rubber  from 
Central  America  we  generally  in- 
clude the  territory  where  we  find  the 
Castilloas  growing.  This  includes, 
therefore,  not  only  Central  Amer- 
ica proper,  but  also  Colombia,  Ecua- 
dor and  Venezuela,  in  fact,  terri- 
tory north  of  the  Amazon  including 
Mexico.  In  a  previous  chapter  we 
mentioned  certain  rubbers  from 
Ecuador  and  Colombia,  but  now  we 
shall  call  attention  simply  to  the  rub- 
ber obtained  from  the  Castilloas. 

The  rubber  balls  used  by  the  na- 
tives in  the  game  which  Columbus  and 
the  early  exploiters  found  them  play- 
ing was  of  the  Castilloa  variety. 

Varieties 

This  rubber  tree  found  native  in 
Central  America  and  Mexico  is  called 
Castilloa  lactiflua,  in  honor  of  Cas- 


tillo, a  Spanish  botanist  who  died  in 
1793  while  preparing  the  flora  oi' 
Mexico.  Lactiflua  means  flowing 
milk,  distinguishing  it  from  other 
trees  from  which  the  milk  exudes  but 
does  not  flow  freely.  The  tree  gen- 
erally is  called  Castilloa  elastica.  It 
is  a  significant  fact  that  at  one  time 
there  was  more  Central  American 
rubber  used  in  the  United  States 
than  there  was  of  Para.  It 


FIG.   14 — MEXICAN   RUBBER  GATHERER 


FIG.  15 — TAPPING  CASTILLOA 

does  not  possess  the  strength,  tough- 
ness or  elasticity  of  Para. 

The  varieties  of  rubber  from  this 
region  which  are  more  or  less  familiar 
to  the  trade  are  Guayaquil  sheet, 
coming  from  Ecuador  and  Colombia  ; 


18 


CENTRAL  AMERICAN  RUBBERS 


19 


there  is  also  some  Guayaquil  and  Car- 
thagena  strip,  some  in  the  form  of 
sausage,  and  some  designated  as  No. 
1  and  Xo.  2 ;  their  production  is  on 
the  decrease  at  present. 

A  grade  referred  to  as  Mexico 
comes  from  Vera  Cruz,  Tabasco  and 
Baraca.  Guatemala  furnishes  a  rub- 
ber bearing  the  same  name.  These 
rubbers  are  rather  inferior  in  qual- 
ity. It  is  thought  that  they  are 
mixed  up  with  cheap  molasses,  as 
some  are  very  tacky. 

Nicaragua  sheets  and  several  grades 
called  West  Indies,  which  never  fur- 
nish any  rubber,  along  with  Nica- 
ragua scrap  are  familiar  rubbers 
from  this  territory.  The  Nicaragua 
rubber  is  generally  quite  dry  but 
rather  dirty.  The  Greytown  scrap  is 
considered  about  the  best  rubber 
from  this  district. 

In  order  to  encourage  the  produc- 
tion of  rubber  the  government  of 
Nicaragua  gives  a  premium  of  ten 
cents  for  every  rubber  tree  planted 
where  the  number  does  not  go  below 
two  hundred  and  fifty  planted  for 
each  person.  The  trees  must  be 
planted  sixteen  feet  apart. 

Virgin  or  Virgen  comes  in  the  form 
of  strip  and  sheet  and  slab.  It  is 
obtained  from  a  different  tree  than 
the  others  mentioned  above  and  is 
used  to  a  great  extent  in  the  manu- 
facture of  hard  rubber. 

Guayule  is  a  rubber  from  this  sec- 
tion unique  in  its  growth  and  pro- 
duction. 

The  above  comprise  the  rubbers 
which  we  shall  consider  in  this  arti- 
cle. The  better  grades  of  Centrals 
shrink  from  25  to  30  per  cent,  and 
the  remainder  from  30  to  40  per  cent. 

The  method  of  obtaining  the  latex 
in  use  in  Central  America  consists 
in  puncturing  rather  than  tapping, 
the  tree  being  punctured  higher  up 
than  is  the  custom  in  the  case  of  any 
other  species  we  have  considered. 

In  order  to  coagulate  the  latex  the 
native  uses  some  very  primitive 
means.  For  instance,  he  sometimes 
adds  to  the  latex  the  juice  of  the 
"  amole  "  vine.  Often  this  is  car- 
ried out  in  a  hole  in  the  ground. 
One  pint  of  amole  juice,  which  is 


FIG.    16 — COAGULATING   WITH   VINE   JCUCR 

alkaline  in  reaction,  is  added  to  one 
and  a  half  gallons  of  latex.  In  a  more 
modern  way,  after  adding  the  juice 
the  wrhole  mass  is  heated  to  between 
165  deg.  and  175  deg.  Fahr.  By  this 
method  they  are  able  to  obtain  sheet. 
The  part  which  dries  on  the  tree 
and  is  peeled  off  is  called  scrap. 

The  Coyuntla  juice  is  an  astringent 
in  nature  which  will  coagulate  the 
rubber  if  the  weed  which  contains 
it  is  used  to  whip  the  latex. 

The  natives  in  some  places  pour 
the  milk  from  the  tree  onto  mats, 
where  it  is  allowed  to  dry  or  evapo- 
rate,'then  wrhen  the  rubber  is  sep- 
arated from  the  mat  a  sheet  results. 
Several  of  these  sheets  are  pressed 
together  and  are  then  ready  for 
market. 

Another  method  similar  to  the  last 
consists  in  pouring  the  latex  out  onto 
the  long,  palm-shaped  leaves  of  the 
Oja  blanca  which  they  have  dried  in 
the  sun. 

When  the  leaves  have  a  coating 
of  about  a  quarter  of  an  inch  they 
are  piled  one  above  the  other  and 
pressed  to  remove  moisture.  The 
strips  are  then  separated  from  the 
leaves,  packed  into  slabs  and  are 
ready  to  be  transported. 


20 


RUBBER    MANUFACTURE 


A  very  common  method  of  coagula- 
tion in  Central  America  is  doubling 
the  volume  of  the  latex  with  water, 
then  allowing  it  to  stand.  In  a  short 
time  I  lie  rubber  comes  to  the  top  in 
a  creamy  consistency.  When  homo- 
genous enough  it  is  removed,  and  in 
some  localities  is  placed  in  the  sun  to 
dry,  while  in  others  it  is  run  through 
between  wooden  rolls  which  press  out 
the  excess  water.  It  is  then  placed  in 
the  sun  for  about  fifteen  days  to  dry 
still  f  lift  her.  This  rubber  suffers  a 
loss  of  as  much  as  50  per  cent,  as  it 
contains  so  much  occluded  water  and 
uncoagulated  la  I  ex. 

All  of  these  rubbers  as  prepared 
by  the  natives  arc  not  of  the  quality 
which  they  might  be  if  more  care 
was  exercised  in  their  production 

Hubber  is  now  being  produced  from 
the  Castilloa  on  a  plantation  scale  at 
different  places.  To  get  an  idea  of 
these  plantations,  AVC  shall  describe 
the  industry  as  we  find  it  in  operation 
by  the  La  Zacnalpa  Rubber  Planta- 
tion Co. 

The  development  of  the  industry 
in  Mexico  is  told  in  a  little  book. 


;i  Rubber,  What  it  Is  and  How  It 
Grows,"  published  by  the  above 
company.  In  describing  this  rubber 
business  we  shall  therefore  use  ex- 
tracts from  this  work. 

The  lands  in  Mexico  suitable  for 
the  production  of  this  rubber  are  lo- 
cated in  the  states  of  Vera  Cm/,  Ta- 
basco, and  Chiapas,  for  the  elevation 
above  sea  level  should  riot  exceed 
five  hundred  feet.  The  low  lands 
along  the  coast  are  the  best,  where 
the  soil  has  a  great  depth  formed  by 
the  deposits  left  by  the  overflowing 
rivers. 

Land  for  a  plantation  is  generally 
selected  which  has  a  virgin  forest 
rather  than  land  which  has  been  un- 
der cultivation.  It  must  be  capable 
of  perfect  drainage  and  yet  pro- 
tected from  overflowing  rivers,  in 
the  above  mentioned  plantation 
there  are  over  ten  thousand  acres  oi 
trees,  averaging  about  four  hundred 
trees  to  the  acre.  These  trees  attain 
a  height  of  from  forty  to  fifty  feet 
and  a  diameter  of  about  twenty 
inches. 

The    Castilloa    begins    to    blossom 


FIG.  17 — PREPARING  KTHIIKH  ON   O.JA   HLANCA  LEAVES 
SPREADING  LATKX  ON  LEAF  PRESSING  OUT  MOISTURE 


CENTRAL  AMERICAN  RUBBERS 


FIG.  19 — PREPARING  RUBBER  ON  OJA  BLANCA  LEAVES 
REMOVING  RUBBER  SHEET  THE    FINISHED    SHEET 


when  it  is  between  five  and  six  years 
old.  Before  blooming  it  sheds  all  of 
its  leaves,  this  taking  place  between 
January  and  April.  When  the  seed 
is  ripened  the  tree  puts  forth  new 
leaves. 

The  planting  of  these  trees  is  very 
interesting.  The  land  is  first  sur- 
veyed into  tracts  of  thirty-three 
acres,  including  avenues  and  streets : 
the  roads  running  north  and  south 
are  called  avenues  and  are  named, 
while  the  ones  running  east  and  west 
are  called  streets  and  are  numbered. 

The  land  is  cleared  by  cutting 
down  the  forest,  and  is  then  burnt 
over.  It  is  then  staked  out  to  allow 
four  hundred  trees  to  the  acre,  and 
at  each  stake  a  mound  of  earth  is 
made  and  the  rubber  seed  planted, 
which  germinates  in  from  eight  to  fif- 
teen days  and  grows  quite  rapidly. 

After  planting,  a  great  amount  of 
work  is  required  to  keep  the  natural 
vegetation  from  choking  out  these 
tender  trees.  After  about  two  years 
the  tree  requires  very  little  atten- 
tion. The  tapping  begins  when  the 


tree  is  between  five  and  six  years  old. 
The  old  method  consisted  in  mak- 
ing a  V-shaped  incision  in  the  tree 
and  placing  a  leaf  under  this  to 
serve  as  a  funnel  and  conduct  the 
milk  into  a  hole  in  the  ground  made 
at  the  foot  of  the  tree.  This  hole 
was  lined  with  green  leaves.  In  a 
short  time  the  latex  coagulates  on 
the  edges  of  the  incision  and  stops 
the  flow.  This  is  removed  as  often 
as  necessary  until  the  milk  ceases  to 
run. 

To  tap  twelve  trees  and  obtain 
their  full  quota  of  latex  is  regarded 
as  a  day's  work  for  one  laborer. 
When  the  flow  has  stopped  the  tap- 
per carefully  removes  the  leaves  con- 
taining the  latex  from  the  hole  and 
pours  it  into  his  gathering  recepta- 
cle. It  is  a  very  wasteful  method  at 
best.  When  some  .of  these  trees  are 
first  tapped  the  milk  will  spurt  out 
some  distance,  just  as  though  it  were 
under  pressure  in  the  tree. 

The  new  method  of  tapping  we 
shall  take  from  the  book  referred  to 
above. 


22 


RUBBER   MANUFACTURE 


"  The  hulero,  or  rubber  gatherer,  is  sup- 
plied with  a  tool  invented  and  perfected 
on  La  Zacualpa  Plantation,  consisting  of 
a  stout  handle,  twelve  inches  long,  at  one 
end  of  which  a  U-shaped  sheet  of  steel  is 
fastened ;  just  forward  of  this  U,  the 
curved  portion  of  which  is  sharpened  to  a 
keen  edge,  a  metal  finger  is  depressed 
more  or  less  as  desired 'by  an  adjustable 
screw  which  runs  through  the  handle ; 
and  the  '  set '  or  '  adjustment '  of  this  fin- 
ger, which  slides  over  the  surface  of  the 
bark  as  the  tool  is  drawn  across  the  tree, 
determines  the  depth  of  the  cut  made  by 
the  U-shaped  knife  which  follows  imme- 
diately behind  the  metal  finger. 

"  A  deeper  or  shallower  cut  may  be 
made  according  to  the  size  of  the  tree 
which  we  are  tapping  and  the  thickness 
of  the  bark ;  and  we  can  effectually 
guard  against  cutting  through  the  bark 
and  into  the  wood  of  the  tree.  The  latex, 
or  rubber-producing  milk,  flows  in  veins 
in  the  bark  only,  and  is  entirely  distinct 
from  the  life  sap  of  the  tree  which  flows 
between  the  bark  and  the  wood.  It  is  im- 
possible to  avoid  cutting  into  the  wood 
when  the  machete  is  used,  and  it  is  from 
the  machete's  too  deep  cutting  that  injury 
to  the  tree  results. 

"  With  our  perfected  tapping  tool  a 
smooth  continuous  channel  is  cut  across 
the  tree's  trunk  and  a  canal  is  made  which 
cannot  fail  to  conduct  the  latex  to  a  re- 
ceptacle placed  to  receive  it ;  while  the 
succession  of  hackings  made  by  the  ma- 
chete are  often  out  of  line  and  much  of 
the  latex  flowing  along  the  cuts  leaves  the 
line  of  travel  and  is  lost." 

The  method  of  treating  the  latex 


on  the  plantation  is  quite  different 
from  the  wasteful  and  dirty  ways  of 
the  natives.  The  exact  process  of  co- 
agulation is  kept  secret,  but  after  it  is 
coagulated  the  rubber  is  washed 
through  a  modern  washer,  sheeted 
and  hung  up  to  dry,  then  by  means 
of  a  hydraulic  press  these  sheets  are 
made  into  solid  blocks  of  about  twen- 
ty-five pounds  each,  when  the  process 
is  complete. 

In  Mexico  a  shrub  is  found  which 
produces  rubber  and  is  not  known  to 
grow  in  any  other  locality.  A  care- 
ful study  of  this  plant  has  been  made 
by  Francis  Ernest  Lloyd,  Professor 
of  Plant  Physiology,  Alabama  Poly- 
technic Institute,  and  from  his  ac- 
count we  get  a  good  idea  of  this  par- 
ticular rubber  plant.  It  bears  the 
name  Guayule  (Parthenium  argenta- 
tum)  and  flourishes  on  the  Chihua- 
huan  Desert. 

It  was  discovered,  by  J.  M.  Bige- 
.low  in  1852,  while  attached  to  the 
Mexican  Boundary  Survey,  and 
was  first  described  by  Prof.  Asa 
rubber  was  first  obtained  from  it  by 
the  natives  by  chewing  the  bark  and 
then  collecting  the  rubber  together  in 
a  ball. 

This  method  of  getting  the  rubber 


FIG.  20 — DENSE  GROWTH  OF  GUAYULE 


CENTRAL  AMERICAN  RUBBERS 


FIG.  20 — A  GUAYULE  EXTRACTING  FACTORY 


dates  back  a  great  many  years.  To 
substantiate  this  belief  Professor  R. 
H.  Forbes  furnished  the  following 
information  : 

"  The  lump  of  rubber,  a  portion  of  which 
I  recently  handed  you,  was  found  in  De- 
cember (or  thereabouts),  1909,  at  the 
\vest  end  of  the  Santa  Cruz  Reservoir  and 
Land  Company's  dam,  14  miles  west  of 
Sasco,  Ariz.  C.  O.  Austin,  who  was  pres- 
ent, states  that  this  ball  of  rubber  was 
contained  in  a  small  olla  with  articles  of 
stone  belonging  to  the  older  prehistoric 
ruins  of  the  country. 

"  The  find  was  made  at  about  three  feet 
below  the  general  surface  which  was 
formed  by  the  off-wash  of  an  adjacent  low 
mountain.  Xo  traces  of  houses  on  the 
present  level  of  the  land,  according  to  Mr. 
Austin,  were  visible.  One  other  ball  of 
rubber  was  found  hero,  and  is  now  in 
Col.  AV.  C.  Greene's  collection  at  Cananea. 
I  regard  this  find  as  genuine,  as  Mr.  Aus- 
tin is  familiar  with  Salt  River  Valley 
ruins  and  bis  statements  are  confirmed 
!>y  others." 

Because  of  the  resinous  content  of 
this  plant  it  burns  rapidly,  and  large 
quantities  of  it  have  been  used  in 
Mexico  as  fuel  in  smelting. 

About  the  first  move  to  utilize  this 
rubber  was  in  1888,  when  a  company 
sent  an  agent  into  Mexico  with  in- 
structions to  obtain  some  of  this 
;'  rubber  bark."  He  carried  out  his 
orders  carefully  and  had  shipped  to 
New  York  100,000  Ib.  of  the  entire 
shrub.  The  freight  on  this  large 
amount  of  wood  so  discouraged  this 
company  that  further  efforts  to  obtain 


this  rubber  were  not  undertaken  im- 
mediately. 

In  1902  a  factory  was  built  at  Ji- 
mulco  for  the  extraction  of  this  rub- 
ber. A  little  later  a  large  factory 
was  built  at  Torreon  by  the  Conti- 
nental-Mexican Rubber  Co.  Since 
this  several  large  factories  have  been 
built  for  extracting  the  rubber  out  of 
the  shrub. 

The  methods  used  for  extraction  of 
this  rubber  are  interesting,  for  they 
are  different  from  any  mentioned 
thus  far;  something  like  it  was  out- 
lined in  connection  with  -the  Lau- 
dolphias,  howrever. 

The  methods  differ  because  the 
rubber  which  the  plant  contains  can- 
not be  removed  by  bleeding,  for  it 
exists  as  rubber  in  the  cells  of  the 
plant  itself.  There  are  two  gen- 
eral methods  which  have  been  and 
are  being  used.  The  first  consists 
in  dissolving  the  rubber  by  means  of 
chemicals  after  the  shrub  has  been 
subjected  to  preliminary  grinding. 

The  other  method  consists  in  ag- 
glomerating the  rubber  mechanically 
after  it  has  gone  through  the  prelim- 
inary grinding.  This  method  has  just 
about  been  abandoned,  as  it  is  impos- 
sible for  it  to  compete  with  the 
mechanical  method.  The  first  process 
consists  in  extracting  the  rubber  from 
the  ground  shrub  by  means  of  naph- 
tha. The  resulting  solution  is  then 


24 


RUBBER  MANUFACTURE 


FIG.  21 — FPPER  FLOOR  IN   GUAYULE  FACTORY 


partly  distilled,  after  which  alkali  is 
added.  This  holds  the  resins  in  solu- 
tion and  the  rubber  separates  out. 

In  the  other  method  the  shrub  is 
pulled  up  root  and  all  and  brought 
to  the  store  houses  for  a  short  period 
of  seasoning,  as  it  seems  to  work 
better  after  such  treatment.  In  the 
more  improved  process  instead  of  pull- 
ing up  the  shrub  it  is  cut  off  at  the 
ground,  and  this  allows  it  to  send  up 
sprouts,  which  in  time  will  produce 
rubber. 

From  the  store  houses  it  is  taken 
and  washed  to  remove  dust  and  s«nd 
which  would  adhere  to  the  rubber 


and  increase  its  specific  gravity.  It 
is  then  passed  between  corrugated 
rolls,  running  differentially,  which 
cut  the  shrub  and  grind  it  at  the  same 
time. 

The  mass  is  then  passed  into  a  peb- 
ble mill,  the  charge  generally  con- 
sisting of  one-third  its  volume  of 
pebbles,  one-half  of  water,  and  from 
six  to  eight  bushels  of  shrub.  The 
mill  rotates  at  the  rate  of  thirty 
revolutions  to  the  minute  for  from 
ninety  minutes  to  two  hours,  when 
there  results  a  fine  pulp  mixed  with 
little  particles  of  rubber. 

This  is  separated  as  well  as  possi- 


FIG.  22 — TROUGHS  TO  COLLECT  EXTRACT  FROM  PLANTS 


CENTRAL  AMERICAN  RUBBERS 


25 


ble  from  the  dirty  water  which  it  con- 
tains and  then  transferred  to  settling 
tanks.  The  rubber  then  conies  to  the 
top  and  is  removed  by  skimming, 
thus  separating  it  from  most  of  the 
riber.  which  water-logs  and  sinks. 
To  clean  the  rubber  still  further  it  is 
often  put  through  a  beater-washer 
and  scrubbed  for  some  time,  when  it 
goes  between  corrugated  rolls  again 
and  scrubbed  for  some  time,  wrhen  it 
sheet  it  and  make  it  ready  for  the 
market.  This  rubber  contains  about 
25  per  cent  of  moisture. 

In  some  places  they  take  this  rub- 
ber just  as  it  comes  from  the  set- 
tling tanks  and  boil  it  with  a  1  or 
2  per  cent,  solution  of  caustic  soda. 


which  will  separate  the  rubber  more 
completely  from  the  fiber,  and  will 
also  reduce  the  per  cent,  of  resin 
which  normally  runs  about  25  per 
cent.  The  resin  has  also  been  re- 
moved by  extracting  the  Guayule 
with  hot  acetone. 

According  to  Weber,  the  Centrals 
suffer     the      following     commercial 

losses : 

Per  cent. 

Guayaquil  (sheet)  20  to  30 

Guayaquil.  Carthagena  ( strip  i...  20  to  30 

Mexico  12  to  15 

Guatemala    25  to  35 

Nicaragua    (sheet) 10  to  15 

Nicaragua     (scrap) 10  to  15 

Virgin   sheets 12  to  15 

Qua  rule    .  30 


CHAPTER  V 


Rubber  Plantations  and  Their  Development 


When  we  consider  plantation  rub- 
ber our  attention  and  thought  are 
directed  to  that  produced  in  Ceylon, 
the  Federated  Malay  States,  Dutch 
East  Indies,  Borneo,  and  the  Pacific 
Islands.  In  this  chapter  we  shall  con- 
sider the  establishment  and  mainte- 
nance of  the  rubber  business  in  these 
areas. 

The  tree  which  is  now  almost  exclu- 
sively planted  upon  these  plantations, 
and  thus  furnishes  the  rubber,  is  the 
Hevea,  the  descendant  of  the  tree 
which  was  first  found  in  South  Amer- 
ica. 

It  was  Herbert  Wright  who  in  1834 
suggested  that  it  would  be  profitable 
to  plant  some  of  the  best  species  of 
rubber  producing  trees  in  the  East 
and  West  Indies,  for  even  at  this  time 
Hancock,  who  was  experimenting  with 
rubber,  was  having  difficulty  in  ob- 
taining the  crude  rubber. 

The  real  plantation  industry  as  we 
know  it,  however,  dates  from  the 
work  of  Sir  Joseph  Hooker,  director 
of  the  Royal  Gardens  at  Kew,  Sir 
Clements  Markham,  connected  with 
the  India  Office,  and  Collins,  Cross 
and  Wickman,  who  made  excursions 
collecting  material. 

In  1873  Collins  obtained  some  seeds 
of  the  Hevea  from  the  Amazon  region 
and  took  them  to  Kew.  In  1875  he 
collected  some  from  the  Castilloa  and 
after  many  trials  and  hardships  suc- 
ceeded in  landing  these  at  Kew.  In 
1877  he  obtained  more  seeds  from  the 
Hevea  and  no  doubt  some  of  the  trees 
in  the  East  to-day  are  direct  descend- 
ants from  these  seeds. 

In  1876  H.  A.  Wickman,  who  was 
living  in  the  rubber  region  of  the 
Amazon,  was  commissioned  by  the 
Indian  Government  to  obtain  a  sup- 
ply of  Hevea  seeds.  The  Govern- 


ment of  Brazil  was  opposed  to  the 
shipping  of  these  out  of  the  country. 

Wickman  fortunately  had  the  op- 
portunity to  charter  a  large  steamer 
which  had  given  up  her  cargo  and 
was  about  to  return  empty.  This  he 
did  and  with  the  aid  of  all  the  laborers 
he  was  able  to  get  he  started  out  to 
collect  the  seeds.  They  succeeded  in 
obtaining  the  supply  and  the  cargo 
was  passed  as  one  of  "  botanical 
specimens. ' '  It  contained  many  thou- 
sand seeds.  These  were  also  taken 
to  Kew,  and  when  planted  only  about 
four  per  cent  germinated. 

Although  the  Indian  Govern- 
ment financed  the  undertaking  they 
selected  Ceylon  as  the  proper  place 
to  carry  out  the  experiment.  The 
principal  nursery  for  trees  in  Ceylon 
was  located  at  Henaratgoda.  Dr. 
Trimen  was  in  charge  of  the  gardens 
and  in  1881  the  first  flowers  were  seen 
upon  these  trees. 

In  1884  there  were  over  one  thou- 
sand trees  there  but  in  1885  the  num- 
ber was  considerably  reduced  owing 
to  the  necessity  of  thinning  out. 

In  1893  over  ninety  thousand  seeds 
were  distributed  to  planters  in  Cey- 
lon, Malaya  and  elsewhere. 

Trimen  made  the  first  experiments 
on  tapping  planted  rubber  trees  in 
1888  and  came  to  the  conclusion  that 
a  big  profit  could  be  realized. 

To  show  how  the  industry  has 
grown  the  following  figures  might  be 
interesting : 

Ceylon 

In  1890  about  300  acres  had  been 
planted;  in  1900  about  1.750  acres;  in 
1904  about  11.000  acres ;  in  1906  about 
100,000  acres,  which  in  1912  was  in- 
creased to  230,000  acres  and  in  1913 
showed  an  acreage  of  235,000 ;  at  pres- 
ent 250.000  acres  have  been  planted. 


26 


RUBBER  PLANTATIONS  AND  THEIR  DEVELOPMENT 


27 


FIG.  23 — HEVEA  SEEDLINGS  READY  FOR  PLANTING 


Malaya 

In  1897  about  350  acres  had  been 
planted;  in  1906  about  100.000  acres 
were  under  cultivation;  in  1912  about 
620,000  acres  had  been  planted.  This 
showed  a  further  increase  in  1913  to 
667.000,  and  is  still  growing. 

Notice  how  rapidly  the  industry  de- 
veloped in  Malaya. 

In  Java  there  are  probably  about 
150,000  acres  planted,  and  in  Sumatra 
about  70,000  acres. 

A  table  showing  the  production  of 
rubber  from  Ceylon  and  Malaya  is 
interesting : 

CEYLON 

YEAR.          EXPORTS. 
Tons. 

1900 147 

1907 IMS 

190S 407 

i  9o9 66C 

1910 1.472 

1911 2.900 

1912 O.c,!»7 

1914 i .-..: :::-;.-, 

1  9ir, .-.  .  .-1.7s.- 

I9io 24.3.-;4 

1917 :;2. 

1918 
1919 

This  gives  some  idea  of  the  great 
business  which  lias  grown  up  so 
quickly. 

Now  we  will  trace  more  in  detail 
how  these  large  plantations  have  been 
established. 


MALAYA 
EXPORTS. 
Tons. 

425 

1.036 

1.665 

3.340 

6.500 

11.000 

18.956 

50.404 

79.415 

111,394 

153.024 

140.659 

240.109 


The  Hevea  was  found  to  grow  in  a 
belt  which  is  included  within  ten 
degrees  of  the  Equator,  provided 
there  was  plenty  of  moisture.  Al- 
though it  flourishes  best  on  the  low- 
lands, it  is  found  giving  good  returns 
at  an  elevation  of  twenty-five  hundred! 
feet.  It  will  grow  in  comparatively 
dry  districts  if  it  is  protected  fronn 
the  wind,  but  of  course  the  growth  is- 
slower  and  a  longer  period  of  time 
is  taken  before  it  is  ready  to  produce- 
any  rubber. 

As  a  general  rule,  we  might  say 
that  rubber  could  be  produced  on- 
almost  any  soil  in  the  latitude  of 
Ceylon  up  to  an  elevation  of  two  thou- 
sand feet,  provided  the  soil  receives 
at  least  seventy-five  inches  of  rain- 
fall a  year.  It  is  found  that  Hevea 
does  best  upon  soil  where  virgin  for- 
ests have  been  removed. 

Planting  Rubber  Trees 

Before  planting,  therefore,  a  greaf 
amount  of  work  must  be  dojie  to  clear 
the  land.  This  is  done  by  cutting 
down  the  trees  and  underbrush  and 
then  burning  it  over  when  it  is  dry. 
In  some  localities,  the  stumps  are  re- 
moved by  means  of  dynamite.  It  is 
found  best  to  remove  all  dead  wootf 


28 


RUBBER   MANUFACTURE 


and  not  allow  it  to  rot  upon  the 
ground,  for  that  removes  the  in- 
creased danger  of  the  young  trees  be- 
ing attacked  by  white  ants  and  root 
diseases.  After  this  land  is  cleared, 
it  requires  a  vast  amount  of  labor  to 
keep  down  the  weeds  which  imme- 
diately spring  up. 

Large  nurseries  must  be  established 
to  supply  the  plantations  with  plants 
which  must  be  at  least  a  year  old 
when  set  out.  The  selection  of  the 
site  for  the  nursery  is  an  important 
matter.  It  must  be  close  to  the  fields 
where  the  plants  will  be  used  and  it 
must  be  in  rich  soil  with  plenty  of 
moisture  and  protected  from  the 
winds.  It  is  not  always  an  easy  mat- 
ter to  find  such  a  site. 

When  planting  the  seeds,  plenty  of 
room  must  be  allowed  for  the  plant 
to  grow.  Generally  seeds  are  placed 
at  a  distance  of  no  less  than  six  by  six 
inches.  Several  times  the  actual  num- 
ber of  plants  needed  should  be  raised 
so  that  only  the  best  may  be  used. 
That  is  the  great  disadvantage  in  the 
method  of  planting  seeds  at  stake 
where  the  plant  remains  whether  good 
or  bad. 

In  the  Malay  States  they  often 
plant  the  seeds  in  individual  baskets 
which  are  later  taken  to  the  planta- 
tion with  the  seedlings  and  planted 
without  disturbing  the  plant  in  the 


least.  This  has  the  same  objection 
as  the  method  of  planting  at  the  stake. 

The  same  area  should  never  be  used 
over  as  a  nursery  unless  it  has  been 
thoroughly  dug  up,  limed  and  then 
allowed  to  remain  fallow  for  some 
time.  This  is  done  to  destroy  all  the 
insect  pests. 

Planters  have  learned  to  realize 
that  great  care  should  be  exercised  in 
selecting  the  seed.  When  a  breeder  of 
cattle  is  desirous  of  producing  beef 
cattle  he  selects  the  largest  of  his  cat- 
tle to  produce  this  strain,  and,  by  con- 
tinued selection,  he  arrives  at  the  de- 
sired result.  If,  on  the  other  hand,  he 
wishes  to  build  up  a  fine  dairy  he  se- 
lects the  ones  from  Avhich  he  gets  the 
largest  amount  of  milk,  and,  by  con- 
tinued selection  of  this  sort,  arrives  at 
a  different  result..  So  it  should  be  in 
the  selection  of  seed  to  produce  the 
rubber  plantation. 

In  the  past  the  planters  have 
striven  to  obtain  their  seeds  from  the 
oldest  trees  regardless  of  whether 
they  produced  much  latex  or  not,  and 
it  has  been  found  that  trees  will  vary 
as  much  in  their  yield  of  latex  as  cows 
will  in  their  production  of  milk.  It 
is,  therefore,  best  to  collect  the  seed 
from  the  trees  which  produce  the  most 
latex,  everything  else  being  equal. 

It  is  not  an  easy  task  on  a  large 
plantation  to  pick  out  a  tree  here  and 


FIG.  24 — WEEDING  YOUNG  RUBBER 


RUBBER  PLANTATIONS  A.\D  THEIR  DEVELOPMENT 


29 


there  and  then  collect  seed  from  these 
trees  only.  So  it  has  been  recom- 
mended that  certain  areas  of  a  planta- 
tion be  set  aside  for  producing  the 
seed  for  future  plantations  ;  that 
these  trees  all  be  tapped  in  the  same 
manner  and  at  the  same  time  and  the 
yield  of  each  tree  carefully  kept. 

After  ascertaining  which  are  the 
best  trees  the  others  are  cut  down 
and  their  stumps  are  drawn  out. 
When  the  time  for  producing  seed 
arrives  the  tapping  is  stopped  and 
the  seed  allowed  to  develop  and  is 
then  collected^  In  this  way  only  seed 
from  the  best  yielding  tree  will  be 
used  and  thus  future  plantations 
should  produce  more  rubber  than  the 
present  ones,  which  have  been  propa- 
gated from  seeds  taken  from  the  oldest 
trees  regardless  of  yield. 

As  to  drainage  there  are  two  dis- 
tinct kinds.  In  the  Malay  States  the 
rubber  is  planted  on  the  low  alluvial 
deposits  where  the  water  level  is  only 
a  foot  or  two  below  the  surface  of  the 
soil;  while  in  parts  of  Ceylon  and 
other  territories  the  trees  are  planted 
upon  steep  hillsides. 

In  the  first  case  the  water  must  be 
removed  to  a  river  or  the  sea,  and  this 
is  effected  by  a  system  of  canals  cut 
through  the  plantations.  This  work 
sometimes  is  done  by  the  govern- 
ment before  the  land  is  leased  or  sold 
for  plantation  purposes,  but  generally 
it  must  be  done  by  the  promoters 
themselves.  In  some  localities  the 
canals  must  be  very  frequent,  in  fact 
between  the  rows  of  trees,  and  the 
trees  are  really  planted  upon  the 
earth  throw],  out  in  the  digging  of  the 


In  the  second  system  drains  are  not 
nit  so  that  the  water  wall  be  removed. 
for  the  natural  slope  will  take  care 
of  that,  but  in  such  a  way  that  the 
water  will  be  removed  so  as  not  to 
wasli  away  the  soil  so  rapidly.  To  do 
this  small  ditches  are  cut  across  the 
slopes  with  a  gentle  fall  and  are  car- 
ried along  until  they  enter  a  natural 
ravine.  The  number  of  such  drains  is 
dependent  upon  the  slope  of  the  land; 
of  course  the  steeper  the  slope  the 
shorter  the  distance  between  them. 
Irrigation  has  been  little  practiced 


as  the  few   attempts   thus   far  made 
have  been  failures. 

The  number  of  trees  to  the  acre  has 
been  a  much  debated  question,  some 
contending  that  best  returns  are  ob- 
tained from  three  hundred  trees  to 
the  acre  and  others  claiming  as  low 
as  fifty,  and  between  these  limits  we 
find  ever}^  conceivable  number  recom- 
mended. 

If  the  trees  are  planted  12  by  12 
feet  apart  we  find  three  hundred  to 
the  acre ;  if  30  by  30  feet  apart  then 
fifty  to  the  acre.  If  the  trees  are 
planted  close  together,  during  their 
early  years  of  tapping  they  are  not 
crowded  and  of  course  more  trees  are 
producing,  but  as  they  get  older  and 
do  become  crowded,  then  their  yield 
when  it  should  have  increased  will  be 
found  to  decrease  and  the  advantage 
is  in  favor  of  the  trees  farther  apart. 
It  is  generally  thought  at  this  time 
that  150  trees  to  the  acre  give  the 
best  results,  though  we  have  not  had 
enough  experimental  data  along  this 
line  as  yet. 

The  planting  is  done  in  holes  about 
a  foot-  and  a  half  deep  at  least,  the 
larger  the  hole  the  better.  In  some 
places  the  holes  are  made  and  the 
ground  loosened  by  the  use  of 
dynamite. 

When  planting,  the  ground  is 
tamped  in  tightly  around  the  seedling 
and  in  some  places  they  are  stumped, 
that  is  the  whole  top  is  cut  away  leav- 
ing just  a  stump.  The  roots  are  also 
cut  off  short  and  the  tap  root  is 
severed.  This  planting  is  done  dur- 
ing the  rainy  season,  and  even  then 
the  young  trees  are  mulched  to  pro- 
tect them  in  case  of  drought. 

The  trees  grow  very  rapidly.  In 
Ceylon  a  Hi  vca  will  grow  from  six 
to  nine  feet  a  year  during  the  first  few 
years  and  its  girth  will  increase  at 
the  rate  of  three  or  four  inches  a 
year.  The  greatest  growth  takes  place 
after  the  third  year  until  the  branches 
become  very  thick:  then  it  grows 
more  slowly. 

In  the  Malay  States  the  growth 
is  more  rapid  and  a  four  years' 
growth  there  is  equivalent  to  a  five 
years'  growth  in  Ceylon.  Some  trees 
in  Cevlon  that  are  about  thirtv-six 


30 


RUBBER   MANUFACTURE 


RUBBER  PLANTATIONS  AND  THEIR  DEVELOPMENT 


31 


years  old  have  attained  a  height  of 
eighty-five  feet. 

Cultivating  the  Land 

The  weeding  which  follows  the 
planting  is  a  vexing  problem  to 
the  planter.  A  great  deal  of  it  of 
necessity  must  be  done  by  hand. 
Some  harrows  drawn  by  oxen  are 
used  but  the  systems  of  drainage  and 
unevenness  of  the  ground  makes  it 
almost  impossible  to  use  any  of  the 
modern  machines  which  recommend 
themselves  for  such  work.  There- 
fore large  numbers  of  coolies  are  em- 
ployed to  remove  the  weeds. 

As  soon  as  the  job  is  completed 
once  they  must  turn  right  around  and 
go  over  it  again,  for  it  becomes  a 
very  expensive  operation  if  the  weeds 
once  get  the  start  of  the  weeders.  It 
is  necessary  to  remove  the  weeds  not 
only  because  they  choke  the  young 
seedlings  but  in  case  of  a  drought 
'they  rob  the  trees  of  the.  moisture 
which  is  imperative  for  their  growth. 

While  the  trees  are  young  and  of 
course  non-productive  it  has  been 
suggested  that  some  other  smaller 
crop  be  grown  between  the  trees. 
This  practice  is  called  "  intercrop- 
ping." Tea  has  been  raised  and  also 
coffee.  Indigo  has  been  recommended 
and  at  first  thought  seems  reasonable 
as  it  is  a  leguminous  plant  and  thus 
collects  nitrogen  from  the  air.  But 
the  synthetic  indigo  has  driven  the 
natural  product  out  of  the  market. 

Many  are  of  the  opinion,  however, 
that  intercropping  is  a  bad  practice, 
as  it  checks  the  growth  of  the  trees 
and  what  is  gained  from  the  inter- 
crop is  lost  when  it  comes  to  the  main 
industry,  the  production  of  rubber. 
When  an  intercrop  is  cultivated  and 
then  dies  as  a  result  of  the  trees' 
shade  it  must  all  be  cleared  away  so 
that  it  does  not  furnish  a  center  for 
the  development  of  fungus  diseases. 

The  use  of  artificial  fertilizers  is 
believed  to  be  advantageous.  Potash 
has  been  found  to  produce  a  better 
growth  in  the  tree  and  also  seems  to 
help  the  renewal  of  bark  where  it  has 
been  removed  in  tapping. 

Too  much  nitrogen  is  a  bad  thing 
as  it  tends  to  make  the  trees  brittle 
and  also  top-heavy.  Nitrogen  is 


necessary  for  plant  growth  and  is  the 
most  expensive  to  supply  to  the  soil 
in  commercial  fertilizers.  To  obtain 
nitrogen  in  soils  which  have  become 
depleted,  therefore,  they  resort  to 
what  is  known  as  ' '  green  manuring. ' ' 
Leguminous  plants  are  sowed  broad- 
cast over  the  freshly  cultivated 
ground.  These  plants  as  they  grow 
take  up  nitrogen  from  the  air  and 
make  it  available  for  plant  use.  These 
plants  must  be  cut  at  the  proper 
stage,  however,  generally  at  intervals 
of  from  four  to  five  months. 

As  the  trees  grow  larger  there 
comes  the  question  of  pruning  and 
thinning.  Very  little  pruning  is  done 
other  than  to  remove  the  dead 
branches  or  ones  that  are  found  low 
down  on  the  trunks  of  the  trees  which 
have  been  planted  far  apart. 

Thinning  presents  a  serious  prob- 
lem. Just  what  trees  shall  be  re- 
moved! Of  course,  the  weakest  ones 
or  those  diseased  should  be  cut  down, 
but  this  often  breaks  up  the  regularity 
in  the  spacing  of  the  trees.  A  careful 
record  of  each  tree  should  be  kept  and 
those  yielding  the  largest  amount  of 
latex  should  always  be  kept,  regard- 
less of  position  in  the  plantation.  Here 
again  all  signs  of  the  removed  trees 
must  be  destroyed. 

Tapping  the  Trees 

At  the  age  of  from  four  to  six  years 
the  trees  have  ttecome  large  enough  to 
be  tapped  and  begin  to  yield  a  small 
return.  At  this  age  the  workers  go 
through  the  plantation  and  measure 
the  trees  to  ascertain  what  ones  are 
suitable  for  tapping.  Any  tree  which 
has  a  girth  of  eighteen  inches  three 
feet  above  the  ground  is  marked  for 
tapping.  Trees  of  this  size  have  bark 
thick  enough  so  that  it  Avill  renew  and 
the  tapping  will  not  permanently  in- 
jure the  tree. 

After  the  trees  are  selected  for 
tapping  the  operation  becomes  purely 
a  routine  one.  The  laborer  starts  out 
earh-  in  the  morning  and  taps  the 
trees  allotted  to  him,  at  this  time  plac- 
ing the  little  cups  in  position  to  col- 
lect the  latex. 

When  the  trees  are  through  run- 
ning, which  is  determined  by  sending 
out  inspectors,  the  tapper  then  re- 


32 


RUBBER   MANUFACTURE 


visits  the  trees  which  he  tapped,  tak- 
ing with  him  two  large  enameled 
buckets.  Into  the  one  he  pours  the 
latex  from  the  cups;  in  the  other 
bucket  lie  lias  a  small  amount  of 
water  in  which  he  washes  the  cup  and 
inverts  it  beside  the  tree  so  that  it 
will  be  clean  and  ready  for  the  next 
day's  use. 

When  this  is  done  he  takes  his  latex 
to  the  central  collecting  station  or  in 
some  cases  directly  to  the  coagulating 
house.  This  in  brief  constitutes  the 
routine  life  of  a  rubber  gatherer. 

The  different  methods  of  tapping 
on  the  plantation  have  been  studied  to 
some  extent.  There  are  two  general 
terms  in  use  for  this.  ' '  Incision  ' '  is 
done  by  puncturing  the  bark,  while 
"  excision  "  means  the  removing  of 
some  of  the  bark. 

Several  "  incision  "  methods  have 
been  used  and  are  still  in  use.  There 
was  at  first  a  practice  copied  after 
the  natives'  method,  of  making  a 
large  gash  in  the  tree.  Later  two 
gashes  were  joined  together  in  the 
shape  of  a  V. 

Then  the  practice  of  pricking  the 
bark  was  tried.  A  good  flow  of 


FIG.    2(5 — MARKING    TREES    FOR    TAPPING 


latex  was  secured  and  the  recovery- 
was  rapid,  but  it  took  too  much  time 
to  perform  the  tapping  and  the  latex 
was  difficult  to  collect.  The  former 
difficulty  was  removed  when  Bowman 
recommended  his  rotating  spur- 
shaped  pricker.  A  single  stroke  with 
one  of  these  tools  would  make  a  row 
of  incisions  running  across  the  bark 
of  the  tree.  The  latex  was  hard  to 
collect  so  they  combined  this  method 
with  the  one  of  making  a  shallow 
channel  in  the  bark  to  carry  the  latex. 
This  however  seems  to  injure  the 
trees. 

In  Ceylon  they  tried  tapping  by 
use  of  the  herring-bone  system  where 
each  rib  was  not  a  channel  but  four 
ribs  made  by  a  pricker.  With  the  aid 
of  a  tapper,  the  latex  can  be  made 
first  to  follow  into  the  central  channel 
and  thus  be  collected. 

Bamber  suggested  a  method  of  inci- 
sion which  produces  large  quantities 
of  latex.  He  made  two  vertical  chan- 
nels 011  opposite  sides  of  the  tree ; 
then,  beginning  at  the  top,  he  made 
transverse  cuts  from  one  to  the  other 
extending  to  the  bottom.  He  would 
skip  a  day  then  make  his  vertical 
sections  an  inch  to  the  right  of  ill- 
original  ones  and  tap  the  tree  in  tin- 
same  manner.  This  was  repealed 
until  the  whole  circumference  of  the 
tree  had  been  tapped.  This  method 
has  the  objection  first  of  consuming 
a  large  amount  of  time ;  second,  that 
the  trees  when  fully  tapped  must  be 
allowed  a  rest  period ;  and  third,  that 
a  large  amount  of  rubber  coagulates 
on  the  tree  and  must  be  collected  as 
scrap. 

At  present  nearly  all  the  tapping 
is  done  by  "  excision  "  methods,  or 
the  removing  of  the  bark. 

The  exact  time  depends  somewhat 
upon  the  length  of  time  given  for  the 
removal  of  the  bark.  Four  year> 
seems  to  be  the  average  time  allowed 
for  this,  although  there  is  a  common 
belief  that  a  longer  time  should  be 
allowed.  But  when  four  years  is  de- 
cided upon,  the  circumference  of  the 
tree  is  divided  into  four  equal  parts, 
and  each  quarter  tapped  by  the  half- 
herring-bone  method.  Each  qua  Her 
Ilien  represents  a  year's  tapping.  To 
preserve  the  symmetry  of  the  tree  the 


RUBBER  PLANTATIONS  AND  THEIR  DEVELOPMENT 


quarter  opposite  the  one  first  tapped 
is  tapped  the  second  year  and  the 
other  two  sections  in  successive  years. 
To  mark  the  tree  for  tapping,  a 
horizontal  line  is  marked  around  the 
tree  about  four  feet  from  the  ground. 
From  this  line  just  five  inches  apart, 
if  the  tree  has  a  girth  of  twenty 
inches  at  this  point,  two  vertical  lines 
are  marked  down  the  tree.  Then  five 
inches  down  on  one  line,  a  -point  is 
marked  and,  when  a  line  is  drawn 
from  this  point  to  the  intersection 
of  the  other  vertical  line  with  the 


KKI.    -~     HAM -HKRKI.NGBOM.  TAPPING 

horizontal  one.  it  makes  an  angle  of 
45  deg.  with  the  vertical  ones.  This 
establishes  the  angle  for  cutting  and 
removing  the  bark. 

The  one  vertical  line  is  now  made  a 
broad  deep  channel  for  conducting 
the  latex,  and  the  other  is  made  deep 
enough  to  preserve  the  limits  of  the 
year's  tapping.  Along  the  oblique 
line,  a  groove  is  cut  deep  enough  to 
allow  the  latex  to  flow  and  not  to  in- 
jure tlie  cambium. 


That  operation  constitutes  the  first 
tapping.  On  alternate  days  gen- 
erally another  thin  slice  of  bark  is 
removed  from  the  lower  edge  and  thus 
the  process  goes  on  until  the  season 
of  tapping  is  over  and  by  that  time 
the  bark  has  been  removed  from  this 
quarter  of  the  tree.  Great  skill  is 
acquired  by  some  of  the  workers  in 
this  form  of  tapping.  From  the  fol- 
lowing table  some  idea  of  the  amount 
of  rubber  produced  per  acre  can  be 
gained : 


of  trees. 

Years. 

4-5 

5-6 

G-7 


, CEYLON. N     ,— MALAYAN.-^ 

Per  acre.  Per  tree.  Per  acre.  Per  tree. 


7-* 


Lbs. 
50 
100 
150 
200 
250 
300 


Lbs. 
A 
.0 
.8 

1.2 

1.5 

1.9 


Lbs. 
100 
150 
200 
250 
350 
400 


Lbs. 
.8 
1.0 
1.3 
1.6 
2.2 
2.5 


(This  table  is  taken  from  the  report  of  It.  II. 
Lock. ) 

Coagulating  the  Latex 

We  shall  next  discuss  the  handling 
of  the  latex  which  generally  contains 
about  thirty-five  per  cent  caoutchouc. 
This  latex  is  brought  into  the  place  of 
coagulation  either  in  large  enameled 
buckets  on  the  heads  of  the  gatherers 
or  it  may  be  brought  by  them  simply 
to  a  collecting  station  in  this  manner 
and  from  there  sent  by  a  railroad  sys- 
tem to  the  factory  for  treatment. 

The  first  process  is  that  of  coagula- 
tion. 

The  substance  used  to  the  greatest 
extent  for  this  purpose  is  acetic  acid. 
Tt  is  said  that  99^  per  cent  of  the 
plantation  rubber  is  coagulated  by 
this  reagent.  The  amount  to  be  used 
varies  considerably  but  fortunately  if 
may  be  used  through  quite  a  range 
and  not  impair  the  rubber. 

Some  one  has  suggested  that  an 
indicator  like  litmus  be  added  to  the 
latex,  which  is  alkaline,  then  add  the 
acid  until  it  shows  an  acid  reaction. 
This  has  not  been  found  to  work 
satisfactorily  in  the  hands  of  inex- 
perienced labor.  Then  too  the  latex 
varies  and  in  some  instances  that 
amount  of  acid  is  not  sufficient  to 
cause  coagulation  as  rapidly  as 
desirous. 

The  safest  rule  is  to  make  pre- 
liminary tests  on  each  batch  of  latex 
and  thus  ascertain  just  how  much 
acid  is  required  to  produce  the  best 
results.  No  rule  of  thumb  is  found 


34 


to  work  in  all  cases.  Perkin  recom- 
mended the  use  of  one  part  of  acetic 
acid  to  eleven  hundred  parts  of  latex. 
The  acid  is  first  measured  out  and 
then  diluted  with  water  when  it  is 
added  to  the  strained  latex  and 
thoroughly  stirred,  then  allowed  to 
stand  for  a  length  of  time  depending 
upon  what  form  the  finished  rubber  is 
to  be  in. 

If  crepe  is  being  made  the  spongy 
rubber  is  removed  after  it  has  stood 
about  half  an  hour  and  is  transferred 
to  a  washing  machine. 

If  sheet  is  to  be  made  it  is  coagu- 
lated in  shallow  pans.  These  are 
allowed  to  stand  until  the  rubber  is 
firm  and  can  be  removed  in  one  sheet. 
This  generally  takes  several  hours. 
These  sheets  are  then  passed  between 
smooth  rolls  running  at  the  same  rate 
with  a  stream  of  water  playing  over 
them.  This  is  to  remove  the  traces  of 
acid  which  remain  after  the  coagu- 
lation. 

When  preparing  crepe  the  washing 
is  done  upon  a  machine  which  has 
corrugated  rolls  and  these  run  at  dif- 
ferent speeds.  The  rubber  comes  out 
in  a  long  lace-like  strip  which  will 
dry  quickly  and  is  then  ready  for 
packing. 

The  drying  is  done  by  one  of  two 
methods.  The  rubber  may  be  hung  in 
an  airy  room,  from  wThich  the  light 
must  be  excluded,,  and  allowed  to  re- 
main there  until  it.  is  dry.  In  moist 
climates  this  takes  a  long  period  of 
time.  To  shorten  the  time  hot  air  has 
been  blown  into  these  rooms,  and  thus 
the  drying  hastened.  Prolonged  ex- 
posure of  the  rubber,  however,  to  a 
high  temperature  often  renders  it 
tacky. 

As  a  still  quicker  method  vacuum 
driers  have  been  used.  Some  manu- 
facturers contend  that  the  life  or 
nerve  of  the  rubber  is  killed  by  dry- 
ing in  a  vacuum.  This,  however,  is  a 
debatable  question. 

The  crepe  after  being  vacuum  dried 
is  then  run  through  a  machine  which 
you  might  say  recrepes  it,  for  the 
vacuum  drier  tends  to  make  it  fluffy. 
In  some  places  in  connection  with  the 
slow  drying  process  they  have  imi- 
tated the  smoked  rubber  from  South 


America  by  blowing  the  smoke  from 
burning  green  wood  or  cocoanut  husks 
into  the  drying  rooms  where  either 
the  crepe  or  sheets  may  be  hanging. 
Rubber  treated  in  this  manner  is 
known  as  smoked  crepe  or  sheet  and 
has  been  at  a  premium  in  the  market. 
Machines  and  methods  for  smoking 
the  latex  directly  have  been  patented 
from  time  to  time  but  as  yet  none  of 
these  are  used  to  any  extent. 

Block  rubber  is  made  by  pressing 
together  either  smoked  or  unsmoked 
sheet  or  crepe.  In  this  form  it  is 
handled  conveniently  but  when  it 
comes  to  the  factory  for  use  it  must 
be  cut  up,  which  takes  labor,  and  then 
too  it  may  contain  objectionable  sub- 
stances in  its  interior. 

The  highest  grade  of  rubber  is  pre- 
pared from  strained  latex  and  is 
known  as  first  latex  rubber. 

On  the  large  plantations  the  scrap, 
that  which  is.  coagulated  upon  the 
trees  and  collecting  receptacles,  is 
worked  up  first  oft  masceratiiig  ma- 
chines, then  wasjiechand  comes  out  in 
a  form  of  crepe  wfr&h  is  graded  ac- 
cording to  its  color. 

Tree  Diseases  and  Other  Pests 

It  is  well  perhaps  that  we  should 
call  attention  to  some  of  the  pests 
with  which  the  rubber  planter  must 
contend. 

The  one  that  causes  most  trouble  is 
one  over  which  man  has  not  much 
control,  .namely  the  wind.  Hevea 
trees  cannot  be  grown  in  wind-swept 
districts  unless  the  planter  is  able  to 
establish  a  barrier  or  wind  break. 

The  animals  which  are  a  great 
nuisance  are  elephants,  deer,  cattle, 
pigs,  monkeys,  and  porcupines.  If 
you  will  observe  this  list  carefully 
you  will  undoubtedly  come  to  the  con- 
clusion that  it  would  be  a  difficult 
task  to  fence  against  such  a  menagerie 
as  this. 

Not  much  damage  is  done  to  the 
Hevea  by  boring  insects  as  the  pres- 
ence of  the  latex  protects  the  trees 
from  their  attack.  If  a  fungus 
growth  should  kill  the  bark  in  cer- 
tain areas  then  some  stinging  insects 
will  attack  the  tree  at  these  places. 

A  species  of  white  ants,  however. 


RUBBER  PLANTATIONS  AND  THEIR  DEVELOPMENT 


35 


FIG.  2S — FACTORY  ON  RUBBER  PLANTATION 


must  be  carefully  watched  for.  They 
attack  the  roots  of  the  tree  and  then 
€at  out  the  interior.  Their  presence 
remains  very  often  unsuspected  until 
the  leaves  of  an  apparently  healthy 
tree  all  at  once  wither.  They  can  be 
discovered  by  digging  a  small  trench 
around  the  tree  and  noticing  whether 
there  are  any  passage  ways  leading 
out  to  their  nest  which  is  always  lo- 
cated a  little  distance  from  their  food 
supply.  The  fumes  of  sulphur  and 
white  arsenic  will  kill  them. 

There  is  a  slug  \vhich  seems  to 
flourish  upon  the  latex  of  these  trees 
and  often  does  considerable' damage. 
Painting  a  band  of  tar  about  the  tree 
is  sufficient  to  guard  against  this  pest. 

The  greatest  pests  to  the  planter 
are  those  of  a  fungus  growth.  Some 
attack  the  roots,  some  the  stem  and 
branches  and  even  the  fruit. 

The  fungi  which  attack  the  roots 
are  the  hardest  to  deal  with.  Gen- 
erally their  presence  is  not  discovered 
until  a  few  trees  are  blown  down  due 
to  the  killing  of  the  roots.  All  af- 
fected trees  must  be  destroyed  and 
lime  forked  into  the  soil.  This  treat- 
ment will  kill  the  pest. 

The  diseases  of  the  stem  are  called 
canker.  They  are  fungi  which  de- 
velop under  the  bark  and  tend  to 
destroy  it  in  such  a  way  that  it  softens 
and  rots.  As  soon  as  it  is  discovered 


it  should  all  be  cut  away  and  then 
the  tree  if  allowed  to  rest  will  heal 
over  the  infected  area.  This  same 
fungus  will  spread  over  the  tree  and 
attack  the  seed  pods  causing  them  to 
rot  also. 

"  Pink  disease  "  and  "  die-black  " 
are  terms  familiar  on  the  plantation. 
The  affected  trees  must  be  diligently 
sought  out  and  cared  for  when 
detected. 

Great  care  must  be  taken  to  pre- 
vent the  spread  of  any  of  these  pests, 
and  if  that  is  done  promptly  the  task 
of  controlling  them  is  not  difficult. 

Other  Varieties  of  Rubber  Trees 

Some  other  species  of  rubber  trees 
have  been  tried  in  these  countries. 
For  instance,  Castilloa  had  been  un- 
der trial  in  Ceylon,  the  West  Indies, 
and  New  Guinea,  besides  in  the  loc'al- 
ities  mentioned  in  our  last  chapter. 

The  Mannihot  has  been  tried  and  is 
still  being  worked  to  some  extent.  As 
early  as  1883  there  were  nearly  a 
thousand  acres  of  it  under  cultivation 
in  Ceylon.  The  tapping  is  rather  diffi- 
cult and  it  has  not.  therefore,  met 
with  any  degree  of  favor  from  the 
planter. 

Fitntumia  has  been  tried  on 
plantations  in  Africa  as  we  have 
pointed  out  in  a  previous  chapter. 


36 


RUBBER    MANUFACTURE 


Ficus  elastica,  a  rubber  tree  native 
of  Asia,  has  been  planted  in  Java 
and  Dutch  East  Indies  but  the  yield 
of  rubber  is  so  small  that  in  some  in- 
stances they  have  been  cut  down  and 
Hevea  planted  in  their  stead. 

There  has  been  a  lack  of  uniformity 
in  plantation  rubber  in  the  past,  and 
strange  as  it  may  seem  it  is  the  fault 
of  the  rubber  manufacturers.  The 
planters  are  anxious  to  produce  the 
grade  of  rubber  most  in  favor  with 
the  ultimate  consumer,  whose  speci- 
fications have  been  so  often  changed 
that  the  plantation  managers  have 
been  at  a  loss  to  know  just  what  grade 
is  going  to  suit  the  trade  when  they 
buy  their  next  consignment. 

This  condition  brings  to  our  atten- 
tion more  forcefully  the  fact  that 
the  whole  industry  is  still  in  the  expe- 
rimental stage. 

There  are  those  today  who  are  of 
the  opinion  that  the  plantations  in 
the  East  are  not  going  to  be  able  to 
compete  with  the  West  in  the  future. 
Also  that  when  the  large  acreage  of 


planted  rubber  trees  are  matured  and 
come  into  full  production  there  wilL 
be  so  much  crude  rubber  on  the  mar- 
ket that  it  will  not  pay  a  return  suffi- 
cient, to  justify  the  continuance  of 
the  industry.  However  that  may  be 
we  know  that  condition  is  not  bother- 
ing us  at  present. 

The  labor  condition  is  becoming  a 
very  serious  question  on  these  planta- 
tions. A  great  many  of  the  laborers- 
arc  imported  from  India  and  Java,  to 
such  an  extent  that  these  two  gov- 
ernments are  taking  steps  to  stop  lin- 
e-migration of  their  people. 

The  native  of  the  Malay  States  is 
not  of  much  value  in  the  industry. 
He  is  too  proud  and  lazy  to  work  un- 
der the  direction  of  a  superior.  1 1 
some  task  is  given  him  where  he  feels 
independent  he  will  work  fairly  well. 

The  Chinese  have  been  brought  to 
the  plantation  and  they  are  somewhat 
of  the  same  temperament  with  the  ex- 
ception that  they  are  more  in- 
dustrious and  soon  come  to  value  too- 
hisrhlv  their  services. 


FIG.  29 — VACUUM  DRYING  ON  A  PLANTATION 


CHAPTER  VI 


Discussion  of  Colloids 


Rubber  belongs  to  one  of  those  com- 
plex systems  of  matter  known  as  col- 
loids, which,  because  of  their  com- 
plexity, have  been  left  comparatively 
untouched  while  the  more  promising- 
fields  were  being  worked.  Recent 
years  have  seen  a  change  in  this  at- 
titude, so  that  we  are  now  in  pos- 
session of  theories  which,  although 
investigators  differ  in  their  inter- 
pretation, are  very  hopeful. 

We  are  no  longer  held  back  by 
Oraham's  view  that  "  they  (crystal- 
loids and  colloids)  appear  like  dif- 
ferent worlds  of  matter  and  give  oc- 
casion to  a  corresponding  division  of 
the  science  of  chemistry."  Physical 
chemists  are  now  unanimously  agreed 
that  crystalloids  and  colloids  are  not 
different  kinds  of  matter,  but  are 
rather  different  states  of  matter  — 
that  the  same  may  be  obtained  in  the 
one  state  or  the  other  depending  upon 
the  necessary  physical  conditions  of 
homogeneity  as  opposed  to  hetero- 
geneity. We  may  therefore  define 
colloid  chemistry  as  that  branch  of 
the  science  having  to  do  with  hetero- 
geneous systems  of  small  particles. 
globulets,  films,  etc.  A  brief  outline 
of  colloids  is  in  order. 

For  the  colloid  state  at  least  two 
phases  must  be  present.  That  phase 
which  is  divided  and  distributed  (the 
internal  phase)  is  known  as  the  Dis- 
persed Phase  ;  the  external  or  con- 
tinuous phase  as  the  Dispersing 
Medium.  We  may  therefore  postu- 
late eight  simple  types  of  colloidal 
solutions,  namely: 


Dixpcrsffl 
Medium.  Tlinse.  Example. 

<  Jas  ..........  Gas  ..........  Impossible,  since 

all  gases  are 
miscible  in  all 
proportions. 

Gas  ..........  Liquid  ........  Clouds,   mist. 

Gas  ..........  Solid  .........  Smoke,  dust. 

Liquid  ........  fias  ..........  Foam. 

Liquid  ........  Liquid  ........  Emulsions. 

Liquid  ........  Solid  .........  Suspensions. 

Solid  .........  Gas  ..........  Pumice. 

Solid  .........  Liquid  ........  Some  gels. 

Solid.  .  .  .  Solid  .........  Alloys. 


Brownian  Movements 

Let  us  take  a  simple  case  of  sus- 
pension. If  we  throw  a  stone  into 
the  water  it  sinks  rapidly;  broken 
up  it  sinks  less  rapidly.  This  has 
led  to  a  statement  that  the  rate  of 
sinking  is  dependent  upon  the  size 
of  the  particles,  which  is  only  true 
to  a  certain  point.  If  we  go  far 
enough  in  our  subdivision  we  come 
to  the  point  where  the  Brownian 
movements  in  the  suspension  are 
stable  indefinitely,  if  other  conditions 
which  will  be  explained  later  are  sat- 
isfactory. The  Browmau  movements, 
so  called  because  of  their  discovery 
by  R.  Brown  in  1826  (Phtia.  Mag.  4, 
101,  1826),  are  just  noticeable  in 
particles  about  0.01  mm.  in  diameter. 
Their  nature  may  be  readily  observed 
by  stirring  a  very  little  of  an  in- 
soluble fine  organic  powder,  for  ex- 
ample, carmine,  with  water  and 
examining  under  a  microscope.  The 
larger  particles  will  be  seen  to  have 
a  fairly  regular  oscillatory  motion, 
while  the  finer  particles  take  a  more 
zig-zag  course.  Zsigmondy  (Ziir 
Erkentniss  der  Kolloide,  page  107) 
gives  the  following  figures  for  the 
amplitudes  of  these  oscillations  for 
gold  hydrosols : 


Diameter. 

UU. 

6 

10 
35 


A  mplititde. 

p 

10 

3-4 

1-7 


(Of  course,  the  amplitude  and 
velocity  vary  inversely  with  the  vis- 
cosity of  the  dispersing  medium.) 

These  Brownian  movements  are 
usually  explained  by  the  kinetic 
theory  first  advanced  by  Ramsey 
(Chem.  News  65,  30,  1892),  or  some 
modification,  as  being  due  to  the 
bombardment  of  the  particles  in  sus- 
pension by  kinetic  vibration  of  the 
molecules  of  the  medium.  This  ex- 
planation implies  that  all  the  energy 
possessed  by  the  particles  is  derived 


38 


RUBBER   MANUFACTURE 


from  the  medium ;  on  the  other  hand, 
there  is  good  reason  to  believe  that 
it  may,  at  least  in  part,  be  due  to  in- 
trinsic energy  of  the  particles  them- 
selves. 

Characteristics  of  Sols 

Colloidal  solutions  are  distinguished 
from  what  we  ordinarily  recognize  as 
true  solutions  by  the  following  char- 
acteristics : 

1 — Osmotic  pressure  negligible. 

2 — Diffusion  negligible. 

3 — Conductivity  of  medium  un- 
changed. 

4 — Elevation  of  the  boiling  point 
not  measurable. 

5- — Depression  of  the  freezing  point 
not  measurable. 

6 — Peptized  or  pectized  by  various 
salts,  ions,  electrical  charges,  etc. 
(Graham  suggested  the  use  of  the 
word  peptonize,  which  because  of  its 
use  in  biology  has  been  changed  to 
peptize  to  indicate  the  change  from 
gel  to  sol  and  pectize  to  indicate  the 
reverse  change.) 

7 — Optical  characteristics  showing 
distinct  heterogeneity. 

The  question  of  whether  or  not  col- 
loidal solutions  differ  from  true  or 
molecularly  dispersed  solutions  only 
in  'the  size  of  the  molecule  has  been 
much  debated.  The  writer  feels  that 
the  difference  of  opinion  simmers 
down  to  the  interpretation  of  per- 
sonal mental  picture  rather  than  any 
real  difference  in  constitution.  On 
the  one  hand,  there  are  some  who  con- 
ceive a  particle  as  made  up  of  a  group 
of  molecules  held  together  by  un- 
known physical  forces,  probably  the 
same  as,  or  analogous  to,  electrical 
forces ;  on  the  other  hand,  others  con- 
ceive the  particle  as  a  molecule  held 
together  by  much  the  same  forces  as 
are  the  various  atoms  which  in  turn 
are  much  the  same  as,  or  analogous 
to,  electrical  forces.  The  latter  ex- 
plains the  low  osmotic  pressure  and 
non-diffusion  by  the  size  of  the  par- 
ticles, the  low  conductivity,  and  the 
little  influence  on  boiling  or  freezing 
points  to  the  relatively  small  number 
of  molecules  in  a  given  volume  of  the 
solution. 


FIG.    30 — OLIVE-OIL — WATER    EMULSION 

VlSCOSITY   CUBVE 

The  former  points  to  examples  such 
as  soap;  in  water,  the  various  char- 
acteristics of  true  solutions  may  be 
slightly  observable  due  to  alkali  pres- 
ent either  free  or  as  the  result  of 
hydrolysis,  but  they  are  negligible; 
on  the  other  hand,  alcohol  solutions 
of  soap  behave  perfectly  normally  in 
every  respect. 

Still  another  case  is  that  of  olive 
oil-water  emulsions.  Starting  with 
either  as  external  phase,  there  is  a 
fairly  gradual  increase  in  viscosity 
until  we  get  to  about  80  per  cent 
olive  oil  and  20  per  cent  water,  at 
which  point  the  viscosity  increases 
abruptly  until  it  reaches  a  very  high 
point.  This  may  be  explained  by  a 
chemical  combination  of  olive  oil  with 
water  at  this  point.  Looking  at  it 
from  the  purely  physical  side,  why 
should  not  the  two  combine  when 
the  other  is  in  excess  and  give  a 
smooth  curve?  Explaining,  can  we 
not  conceive  of  putting  globulets  of 
oil  in  water  or  water  in  oil  until  the 
point  is  reached  where  the  external 
phase  is  not  sufficient  in  volume  to 
reach  around  the  internal  phase  and 
a  rupture  must  take  place,  the 
medium  constituting  external  force 
to  become  the  internal  phase  or  vice 
versa?  The  force  required  to  neu- 
tralize the  surface  tension  of  the  ex- 
ternal phase  and  produce  the  rupture 
would  be  amply  sufficient  to  account 
for  the  abnormality  in  viscosity. 

Surface  Tension 

The  condition  of  heterogeneity  im- 
plies surface  at  the  interface.  The 
writer  has  found  the  following  mental 
picture  very  helpful  in  the  interpreta- 
tion of  the  phenomena. 

We  learned  in  our  study  of  physics 


DISCUSSION  OF  COLLOIDS 


39 


that  every  body  of  matter  attracted 
every  other  body ;  this  applies  to  the 
smallest  particle,  even  to  the  atom. 
The  extent  of  this  attraction  is  repre- 
sented by  the  formula, 

k  m-,  ma 

r~ 

where 

F  is  the  attractive  force, 
m^  and  mz  the  mass  of  the  respective 

bodies, 

r  the  distance  separating  the  bodies, 
k  is  the  constant. 

Because  the  mass  of  the  earth  is  so 
great  and  we  are  so  accustomed  to  in- 
terpret it  in  terms  of  bodies  separated 
by  microscopic  rather  than  submicro- 
scopic  distances  we  are  apt  not  to 
appreciate  its  true  significance  unless 
it  is  called  to  our  attention.  Upon 
inspection,  however,  it  is  realized  that 
as  r  becomes  extremely  small,  even 
though  the  mass  of  respective  bodies 
is  very  small,  the  extent  of  this  force 
may  become  very  great  indeed,  even 
approaching  infinity  as  r  approaches 
zero,  which  it  probably  does  not  do 
even  on  the  interior  of  the  atoms 
themselves.  This  force  may  well  be 
the  force  which  holds  bodies  together ; 
indeed,  it  may  well  be  the  source  of 
chemical  valence. 

The  distance  through  which  this 
force  may  operate  is  very  indefinite, 
but  the  sphere  limiting  its  radius  of 
action  is  at  least  larger  than  the  par- 
ticle itself.  Other  particles  within 
the  sphere  of  attraction  affect  it  and 
are  affected  by  it;  those  outside  do 
not.  Let  us  then  single  out  a  mole- 
cule in  the  interior  of  a  liquid.  It 
exerts  a  sphere  of  attraction  equal 
in  all  directions.  (In  speaking  of 
this  sphere  of  attraction,  we  do  not 
necessarily  wish  to  imply  a  perfect 
sphere.  If  the  molecule  happens  to 
be  a.  chain  structure,  the  sphere 
would  follow  the  general  contour  of 
the  chain.)  Within  this  sphere  there 
will  be  other  molecules,  approximate- 
ly an  equal  number  in  all  directions, 
which  in  turn  build  up  another 
sphere,  and  so  on  until  we  go  beyond 
the  surface.  A  molecule  at  the  cen- 
ter therefore  has  the  same  counter- 
balancing attractions  from  all  direc- 
tions and  the  net  force  tending  to  dis- 


place it  is  consequently  zero,  causing 
equilibrium  in  the  molecule. 

These  series  of  concentric  spheres 
are  thus  continued  until  we  reach  the 
surface.  The  molecule  on  the  surface 
has  many  molecules  within  the  sphere 
of  attraction  on  the  interior,  but  rel- 
atively few  on  the  exterior.  It  is 
consequently  attracted  to  the  interior 
very  strongly  without  counterbal- 
ancing attraction  from  the  exterior. 
The  result  is  a  high  inward  pressure. 
Just  as  a  high  outward  pressure  must 
be  restrained  by  a  high  tension  on 
the  container  walls,  this  inward 
pressure  must  result  in  a  high  sur- 
face compression  in  the  surface  film, 
which  tends  to  cause  the  liquid  to 
decrease  in  volume.  This  surface 
compression  is  incorrectly  known  as 
surface  tension,  and  may  be  observed 
when  \ve  "  heap  "  a  spoon  with 
liquid,  or  float  a  needle  on  the  sur- 
face of  water,  provided  it  is  laid  down 
carefully. 

Any  increase  in  surface  is  attended 
by  an  increase  of  free  energy  at  the 
surface;  conversely,  decrease  in  sur- 
face results  in  a  decrease  of  free 
energy.  Disintegration,  evaporation, 
etc.,  require  energy;  agglomeration, 
condensation,  etc.,  give  up  energy  and 
are  spontaneous.  Large  drops  and 
crystals  grow  at  the  expense  of 
smaller  ones. 

We  have  no  adequate  means  of 
measuring  surface  tension.  It  may, 
however,  be  considered  in  connection 
with  osmotic  pressure,  which,  if  it 
acts  in  any  manner  similar  to  gas 
pressure,  must  require  a  restraining 
force.  What  other  force  than  this 
surface  tension  can  there  be?  And 
since  the  osmotic  pressure  is  outward, 
there  should  be  a  lessening  of  the 
pressure  inward  causing  the  volume 
of  the  solution  to  be  greater  than 
the  volume  of  solvent,  which  always 
happens.  In  the  case  of  some  solu- 
tions, the  osmotic  pressure  is  con- 
siderable ;  the  surface  tension  must 
therefore  be  even  greater. 

Willard  Gibbs  pointed  out  the  ob- 
vious result  of  these  forces;  namely, 
that  there  is  no  definite  boundary 
at  which  the  one  phase  leaves  off  and 
the  other  begins.  True,  the  zone  be- 
tween that  which  is  distinctlv  com- 


40 


RUBBER   MANUFACTURE 


posed  of  the  one  phase  and  that  which 
is  distinctly  composed  of  the  other 
phase  may  be  very  slight;  neverthe- 
less there  is  that  zone  at  every  inter- 
face where  the  two  phases  inter- 
mingle, and  where  surface  forces 
come  into  play.  The  greater  the  sur- 
face tension  the  thinner  the  zone,  i.  e., 
the  less  chance  to  intermingle ;  whence 
it  will  be  seen  that  anything  which 
tends  to  decrease  the  difference  in 
surface  tension  between  two  immisci- 
ble phases  will  cause  them  to  mix 
more  readily ;  the  converse  is  likewise 
true.  This  is  of  great  importance  in 
the  selection  and  use  of  protective 
colloids.  Surface  energy  equals  speci- 
fic surface  times  surface  tension. 

From  the  picture  drawn,  it  is  evi- 
dent that  the  center  of  the  liquid  is 
under  greatest  pressure.  In  the  case 
of  true  or  molecularly  dispersed  solu- 
tions, the  concentration  should  be 
greater  at  the  center,  as  is  found  to 
be  the  case  with,  for  example,  most 
inorganic  salts.  On  the  other  hand, 
where  the  solution  is  only  apparent 
(i.  e.,  heterogeneity),  as,  for  example, 
soap  in  water,  there  will  be  a 
greater  concentration  of  the  solution 
at  the  surface.  Increase  in  surface 
concentration  will  result  in  decrease 
in  surface  tension  and  vice  versa. 
Where  we  have  this  difference  in  con- 
centration between  the  surface  and 
the  interior,  we  have  what  is  known 
as  adsorbtion.  If  the  surface  con- 
centration is  in  excess,  as  is  usually 
the  case,  we  have  positive  adsorbtion. 
If  such  a  solution  is  shaken  with  a 
very  fine  powder  giving  a  very  large 
surface  (size  of  particles  is  not  neces- 
sarily a  criterion,  since,  as  in  the 
case  of  various  blacks,  the  material 
may  be  spongy  and  thus  present  an 
enormous  amount  of  surface  in  the 
capillary  pores)  nearly  all  of  the  solu- 
tion may  be  removed  from  the  sol- 
vent. Surface  deficit  must  necessari- 
ly be  very  slight,  since  the  limit  must 
necessarily  be  pure  solvent  in  the  sur- 
face, which  would  give  rise  to  nega- 
tive adsorbtion  ;  indeed,  even  this  case 
may  be  regarded  as  positive  adsorb- 
tion of  the  solvent. 

Adsorbtion  comes  to  an  equilibrium. 
Thus,  if  a  given  volume  of  solution 
of  certain  concentration  is  shaken 


with  a  weighed  amount  of  adsorbant 
until  equilibrium  is  reached  and  is 
then  diluted,  the  final  concentration 
of  the  solution  will  be  the  same  as 
if  the  dilution  had  been  made  before 
starting.  This  gives  rise  to  the  ad- 
sorbtion equation, 

x  1 

—  =  k  e- 

m  n 

where 

x  is  the   weight   of  substance   ad- 
sorbed, 

m  the  weight  of  adsorbant, 
e  the  volume  of  the  concentration 
after  equilibrium. 

k  and  -  are  constants. 
n 

The  question  as  to  whether  adsorb- 
tion is  chemical  or  purely  physical 
combination  has  been  much  debated. 
Indeed,  the  discussion  simmers  down 
to  a  matter  of  viewpoint.  It  seems 
highly  probable  that  both  forces  are 
akin  to  electrical  attraction  and  there- 
fore may  easily  be  the  same. 

Cataphoresis  and  Electro-endosmos 

In  no  place  does  the  phenomenon 
produced  by  electrical  charge  play 
a  more  important  role.  At  the  inter- 
face between  two  phases  there  is  al- 
ways a  potential  difference.  If  a 
liquid,  say  water,  is  placed  in  two 
vessels  connected  by  a  capillary  tube 
and  subjected  to  electrolysis  it  will 
flow  with  the  current;  if  finely 
divided  particles  of  an  insoluble  pow- 
der such  as  metal,  sand,  etc.,  be  sus- 
pended in  the  liquid,  it  will  move  in- 
stead. This  phenomenon  is  known  as 
cataphoresis.  If  the  flow  is  through 
a  semi-permeable  membrane,  it  is 
known  as  electro-endosmos.  There 
are  three  cases  possible. 

1 — The  particles  are  poor  con- 
ductors and  have  slight  tendency  to 
coalesce.  Such  particles  will  move 
sluggishly  toward  the  electrode  and 
will  congregate  around  it.  Those 
actually  coming  in  contact  with  the 
electrode  will  deposit  a  part  of  their 
charge,  but  not  all  of  it;  the  others, 
being  such  poor  conductors  as  not  to 
be  able  to  transfer  their  charge,  will 
retain  it,  and  when  the  current  stops 
will  mutually  repel  each  other  as  far 
as  possible,  thus  diffusing  themselves 


DISCUSSION  OF  COLLOIDS 


41 


throughout  the  liquid  substantially 
as  before  being  subjected  to  the  in- 
fluence. 

2 — Particles  which  are  good  con- 
ductors but  have  little  tendency  to 
•coalesce  will  move  up  to  the  electrode, 
get  rid  of  their  charge  and  take  on 
one  of  opposite  sign,  after  which  they 
will  start  for  the  other  electrode. 

3 — Particles  which  are  good  con- 
ductors with  a  tendency  to  coalesce 
will  move  up  to  the  electrode,  dis- 
charge, and  be  precipitated. 

We  have  discussed  the  individual 
•conditions  which  bear  upon  colloidal 
phenomena.  We  see  that  colloids  are 
systems  consisting  of  at  least  two  dis- 
tinct heterogeneous  phases,  one  of 
which  is  extremely  finely  divided  and 
dispersed  in  the  other  and  which  is 
more  or  less  affected  by  Brownian 
movements,  depending  upon  the  vis- 
cosity of  the  dispersing  medium.  This 
fine  state  of  division  gives  rise  to  an 
•enormous  extent  of  surface  interface, 
which,  because  of  its  nature,  gives  a 
•correspondingly  large  amount  of  free 
energy  in  form  of  surface  energy  and 
electrical  energy.  The  activity  of 
this  energy  probably  contributes  the 
Brownian  movements  and,  in  being 
neutralized,  gives  rise  to  adsorbtion. 
We  can  postulate  the  behavior  of  so- 
lutions, that  is,  the  conditions  of  pep- 
tization and  pectization. 

Since  the  formation  of  a  large 
amount  of  surface  involves  an  enor- 
mous amount  of  free  energy  which 
is  neutralized  in  part  by  adsorbtion, 
we  have  a  basis  for  Freundlich's  as- 
sertion (Kapilarchemie  52,  154,  1909) 
that  adsorbtion  tends  to  lower  the 
surface  tension  of  the  adsorbing 
phase,  from  which  it  follows  that  any 
substance  which  is  adsorbed  by  an- 
other tends  to  disintegrate  and  pep- 
tize  the  latter.  In  making  this  state- 
ment, however,  we  must  bear  in  mind 
that,  since  adsorbtion  depends  on  the 
surface  and  disintegration  depends 
upon  the  cohesion  between  the  par- 
ticles, there  may  be  no  apparent  con- 
nection between  the  two.  Thus  the 
same  mass  of  porous  material  is  much 
more  easily  disintegrated  than  if  it 
occurs  in  a  more  dense  form. 

Bancroft  (Jour.  Phys.  Chem.  20. 
85,  1916)  has  discussed  this  subject 


in  detail.  He  says:  "  We  may  have 
peptization  by  a  solvent,  by  a  dis- 
solved non-electrolyte,  by  an  ion,  by 
an  undissociated  salt,  by  a  colloid. ' ' 

As  we  raise  the  temperature,  ad- 
sorbtion decreases,  but  the  cohesion 
between  the  particles  also  decreases; 
thus  glass,  coagulated  albumin,  etc., 
are  peptized  by  water,  provided  the 
temperature  is  raised  to  a  point  where 
the  cohesion  between  the  particles  is 
sufficiently  small  to  be  exceeded  by 
the  tendency  to  absorb  the  solvent. 

One  of  the  many  examples  cited 
in  the  case  of  a  dissolved  non-elec- 
trolyte is  the  action  of  sugar  in  pre- 
venting the  precipitation  of  ferric 
hydrate  when  ferric  chloride  is  treated 
with  ammonia. 


OH-  o  H-* 

FIG.  31 — lox  CUKVE 

The  action  of  ions"  is  closely  asso- 
ciated with  their  supposed  electrical 
nature.  If  we  add  a  small  amount 
of  an  electrolyte  to  a  solution,  preci- 
pitation takes  place.  Ions  carrying 
a  charge  opposite  in  sign  to  the  dis- 
persed phase  are  adsorbed  more  rap- 
idly, thereby  neutralizing  the  charge 
which  keeps  them  apart.  Very  soon 
the  place  is  reached  where  the  charge 
which  keeps  the  particles  apart  is  neu- 
tralized, and  instability  results.  Be- 
yond this  point,  the  adsorbtion  of 
the  first  ion  varies  but  slightly  with 
increase  in  concentration,  but  the  ad- 
sorbtion of  the  ion  of  opposite  charge 
increases  until  we  get  a  correspond- 
ing excess  of  the  opposite  charge  and 
consequent  peptization  by  the  salt. 
In  general,  the  action  of  ions  follows 
Schultz's  law  that  the  higher  the 
valence  the  greater  the  influence  of 
a  single  ion.  This  rule  is  disturbed, 
however,  by  the  preferential  adsorb- 
tion of  certain  ions. 


42 


RUBBER   MANUFACTURE 


The  examples  of  peptization  by  a 
colloid  are  without  number  in  our 
every-day  experiences.  "We  have  to 
go  no  further  than  the  use  of  soap 
for  washing;  the  insoluble  dirt  ad- 
sorbs the  soap  film  and  is,  peptized 
by  it,  after  which  it  can  be  easily 
washed  away. 

It  is  not  the  purpose  of  this  work 
to  go  into  the  study  of  colloids.  In 
giving  this  discussion,  the  writer  has 


merely  attempted  an  explanation  of 
some  of  the  fundamental  principles 
underlying  the  behavior  of  colloids 
so  that  their  influence  on  the  rubber 
colloid  may  be  appreciated.  Students 
are  earnestly  requested  to  study  some 
of  the  text  books  and  numerous  arti- 
cles on  colloids,  as  well  as  the  applica- 
tion of  the  principles  to  other  in- 
dustries, such  as  the  cellulose,  glue, 
and  tanning  industries." 


CHAPTER  VII 

Colloidal  Action  of  Crude  Rubber  and  Its  Application  in  Rubber 

Manufacture 


The  latex  as  it  comes  from  the  tree 
is  a  milky  white  fluid  which  in  the 
light  of  colloidal  chemistry  should  be 
classed  as  an  emulsoid  in  contrast  to 
a  suspensoid  ;  namely,  a  heterogeneous 
system  consisting  of  two  distinct 
liquid  phases.  The  dispersing 
medium  is  water  and  the  dispersed 
phase  consists  of  globules  of  ca- 
outchouc ranging  in  size  from  1/x  to 
2/i.  This  emulsion  is  made  fairly 
stable  by  the  presence  of  certain 
resins,  albuminoids,  proteids,  sugars, 
mineral  salts,  etc.,  which  act  as  pro- 
tective colloids.  • 

This  latex  upon  examination  shows 
pronounced  Brownian  movements. 
As  is  the  cast-  in  nearly  all  hydrosols, 
the  dispersed  phase  bears  a  negative 
charge  as  is  shown  when  the  hydrosol 
is  subjected  to  electrolysis,  when  Hie 
globules  migrate  to  the  anode  region. 
From  this  behavior,  we  may  postu- 
late that  upon  the  addition  of  a 
kation,  these  globules  will  tend  to  be 
precipitated  while  the  addition  of 
anious  will  tend  to  make  the  emulsion 
more  stable. 

It  is  quite  possible  that  the 
caoutchouc  itself  in  the  latex  is  posi- 
tively changed,  but  that  it  has  ad- 
sorbed enough  of  the  protective  col- 
loids which  are  negatively  charged  to 
more  than  balance  the  positive  effect 
and  thus  give  to  the  globule  the  effect 
of  being  negatively  charged. 

Therefore  anything  which  tends  to 
destroy  this  protective  colloid,  tends 
to  destroy  the  negative  charge  which 
gives  stability  to  the  emulsion. 

Let  us  now  turn  our  attention  to  a 
discussion  of  the  manner  in  which 
these  principles  are  applied  in  the 
crude  rubber  industrv. 


Preservation  of  Latex 

First  let  us  consider  the  preserva- 
tion of  the  latex  where  it  is  not  de- 
sired to  coagulate  it  immediately.  We 
find  the  general  practice  is  to  add 
ammonia.  This  was  first  done  with- 
out the  knowledge  of  any  scientific 
reason  as  a  basis  for  it ;  now,  however, 
it  may  be  explained  by  the  principle 
which  wre  have  just  mentioned.  The 
ammonia  introduces  hydroxyl  ions, 
bearing  negative  charges  and  these 
tend  to  increase  the  potential  dif- 
ference between  the  two  phases  and 
thus  increase  the  stability  of  the 
emulsion. 

Next,  we  shall  endeavor  to  show 
how  these  principles  are  applied  in 
the  coagulation  of  latex.  To  do  this 
\ve  shall  divide  the  different  means  of 
coagulation  into  the  divisions:  1— 
Mechanical ;  2 — Electrolytic ;  3— 
Dilution;  4— -Natural;  5 — Heat  with- 
out evaporation;  6 — Heat  with 
evaporation  ;  7 — Chemicals. 

In  the  mechanical  coagulation  of 
rubber,  we  simply  take  advantage  of 
the  fact  that  in  the  latex  there  are 
two  distinct  phases  of  different 
density.  Therefore  by  centrifuging 
the  latex,  we  are  able  to  effect  a 
separation.  Rubber  obtained  by  this 
method  compares  favorably  witli  the 
rubber  obtained  by  other  means,  but 
the  process  is  a  tedious  one  and  rather 
expensive  also. 

The  electrolytic  method  is  one  of 
theoretical  interest  only.  As  the  latex 
is  such  a  poor  conductor  of  electri- 
city, and  the  globules  simply  collect 
in  the  region  of  the  anode,  unless  the 
voltage  is  very  high  those  in  actual 
contact  with  the  anode  will  be  the 


-13 


44 


RUBBER   MANUFACTURE 


only  ones  which  will  discharge  and 
thus  precipitate. 

Coagulation  by  dilution  in  a  great 
many  cases  produces  unfortunate 
results,  while  again  it  is  used 
to  advantage.  The  necessity  of 
collecting  latex  out  in  the  open 
in  a  region  where  the  precipitation 
is  so  abundant  makes  dilution  of 
the  latex  by  rain  water  inevitable 
at  times.  Such  latex  coagulates  in 
much  the  same  fashion  as  cream  sep- 
arates from  milk  which  has  been  di- 
luted. Then  in  the  case  of  cup  wash- 
ings, the  latex  which  has  been 
washed  out  from  the  cups  is 
saved.  On  a  few  small  plantations 
where  the  quality  is  not  a  considera- 
tion, and  in  places  where  better  meth- 
ods are  unknown,  this  method  is  used 
as  a  regular  procedure.  The  reason 
for  the  precipitation  undoubtedly  lies 
in  the  fact  that  the  protective  colloids 
are  more  or  less  soluble  in  the  in- 
creased volume  of  the  dispersing 
medium.  When  these  protective  col- 
loids are  removed,  it  results  in  the  pre- 
cipitation of  rubber.  While  compara- 
tively little  is  known  as  to  why  cer- 
tain of  these  materials  which  make  up 
protective  colloids  are  essential,  it  is 
a  fact  that  their  absence  results  in  an 
inferior  product.  Consequently  this 
method  is  by  no  means  satisfactory 
and  is  not  employed  where  its  use  may 
be  avoided. 

When  the  latex  is  allowed  to  stand 
for  some  time,  it  will  coagulate  spon- 
taneously. This  is  110  doubt  due 
to  the  formation  of  acid  in  the  latex 
from  causes  which  will  be  discussed  in 
a  later  chapter.  The  acids  which  are 
produced  furnish  the  necessary  hydro- 
gen ions  to  cause  the  coagulation  of 
the  rubber.  Due  to  the  fact  that  the 
conditions  cannot  be  or  are  not  regu- 
lated correctly,  an  inferior  product 
invariably  results. 

If  the  latex  is  subjected  to  heat 
without  evaporation,  we  have  a  com- 
bination of  results  similar  to  dilution, 
that  is  increased  solubility  of  protec- 
tive colloids,  and  the  formation  of 
acids  as  in  natural  coagulation,  which 
is  probably  still  further  complicated 
by  hydrolysis.  This  method  of  coagu: 
lation  is  of  little  practical  importance. 

When  the  latex  is  evaporated  by 
addition  of  heat,  coagulation  results. 


There  we  have  much  the  same  condi- 
tions as  in  the  case  of  heating  without 
evaporation,  that  is  in  the  formation 
of  acids  and  hydrolysis  but  we  have 
in  this  method  the  advantage  of  uni- 
form conditions  such  as  temperature, 
time,  and  also  the  fact  that  the  pro- 
tective colloids  which  are  soluble  can- 
not be  removed  from  the  rubber. 
Usually,  too,  in  the  case  of  South  Am- 
erican rubbers,  the  process  is  carried 
on  in  the  presence  of  smoke  which 
contains  various  acids  and  alcohols. 
These  tend  to  facilitate  the  coagula- 
tion and  at  the  same  time  inhibit  the 
development  of  bacteria. 

The  foregoing  methods  are  all 
primitive  and  whatever  merits  they 
may  possess  are  accidental. 

Coagulation  by  Chemicals 

By  all  means  the  most  important  is 
the  coagulation  effected  by  chemicals. 
The  ones  in  most  common  use  may  be 
classified  under  the  following  heads: 
Acids,  salts,  alcohols  and  ketones. 

We  would  naturally  expect  all  acids 
to  have  a  coagulating  effect  in  propor- 
tion to  their  degree  of  ionic  dissocia- 
tion since  they  owe  their  power  of 
coagulation  to  the  concentration  of 
hydrogen  ions.  The  question  of  selec- 
tive adsorbtion  plays  no  role  in  this 
because  the  hydrogen  ions  are  the 
same  regardless  of  their  source. 
Strong  acids  should  therefore  be  bet- 
ter coagulants  than  weak  acids  since 
they  possess  a  higher  degree  of  dis- 
sociation. Therefore  we  should  ex- 
pect to  find  the  highest  dissociated 
acids  being  used  for  the  above  pur- 
pose. These  are  muriatic,  nitric,  and 
sulphuric  acids.  In  actual  practice, 
however,  the  first  two  are  not  permis- 
sible. 

.  Muriatic  acid,  while  it  has  the  de- 
sired coagulating  effect,  also  has  a 
deleterious'  effect  upon  the  rubber. 
This  might  be  explained  upon  the 
ground  that  as  a  halogen  acid,  it  acts 
upon  the  polyperene  molecule  at  the 
double  bonds  thus  tending  to  form  ad- 
dition products. 

Nitric  acid  also  possesses  a  marked 
degree  of  coagulation  but  here  the 
strong  oxidizing  power  of  the  acid 
renders  it  useless.  Sulphuric  acid, 
however,  is  used  quite  extensively  as 
it  possesses  neither  of  the  objections 
which  characterize  the  other  two. 


COLLOIDAL  ACTION  OF  CRUDE  RUBBER 


45 


The  question  naturally  arises,  why 
should  acetic  acid  be  used  in  prefer- 
ence to  sulphuric  ?  It  must  be  borne 
in  mind  that  acetic,  however,  is  by  far 
the  strongest  or  most  highly  dissoci- 
ated of  the  so  called  weak  acids.  It 
furnishes,  therefore,  the  necessary 
concentration  of  hydrogen  ions  very 
nearly  as  readily  as  the  sulphuric 
acid.  All  of  either  acid  must  be  com- 
pletely removed  from  the  coagulum. 
Sulphuric  acid  must  be  entirely  re- 
moved by  washing,  and  to  remove  it 
completely  requires  prolonged  wash- 
ing, which  experience  has  shown  im- 
pairs the  rubber.  With  acetic  acid, 
on  the  other  hand,  it  matters  not 
whether  all  the  acid  is  removed  by 
washing  since  any  that  remains  will 
be  volatilized  and  thereby  removed  in 
the  process  of  drying. 

The  other  organic  acids  have  the 
two  objections,  first,  that  they  are  too 
feebly  ionized  and  secondly,  that  their 
cost  makes  them  prohibitive. 

Under  salts,  those  most  commonly 
used  are  sodium  chloride,  alum  and 
soap. 

If  we  apply  the  law  of  Schulze,  that 
is,  that  the  higher  the  valency  of  the 
kations  in  a  hydrosol.  the  greater  will 
be  its  precipitating  power,  then  we 
should  use  those  salts  which  not  only 
furnish  a  high  concentration  of 
katidn  but  also  those  which  possess  a 
large  valence.  Of  course,  this  condi- 
tion may  be  disturbed  by  selective  ad- 
gorbtion. 

We  find  sodium  chloride  is  used 
only  where  the  more  primitive  meth- 
ods are  in  vogue.  It  is  an  extremely 
common  substance  and  consequently 
was  available  for  primitive  experi- 
ments. It  accidentally  possessed  the 
property  of  being  highly  dissociated, 
having  the  necessary  number  of 
kations  to  make  it  effective  as  a  coagu- 
lant. On  the  other  hand,  where  more 
scientific  methods  of  reasoning  have 
been  brought  to  bear,  we  find  alum  is 
used  more  or  less  extensively.  Then 
we  get  a  much  higher  electrical  charge 
with  a  small  number  of  ions.  Soap 
lias  found  little  application  as  would 
naturally  follow  from  what  has  been 
stated  above,  namely :  it  possesses  a 
very  low  degree  of  ionization  and  a 
low  charge  on  the  kation. 


The  use  of  salts  is  in  110  case  de- 
sirable because  if  any  remain  in  the 
rubber  they  will  undoubtedly  under- 
go hydrolysis  and  the  resulting  prod- 
ucts are  likely  to  be  detrimental  to 
the  rubber.  Their  complete  removal 
is  almost  impossible  even  with  exces- 
sive washing. 

In  the  use  of  alcohols  and  ketones 
coagulation  is  effected,  no  doubt, 
because  these  substances  have  the 
power  to  dissolve  the  protective  col- 
loids and  thus  allow  the  rubber  glob- 
ules to  coalesce.  It  is  said  that  a 
much  better  grade  of  rubber  results 
when  either  ethyl  alcohol  or  acetone 
is  employed ;  this  being  no  doubt  due 
to  the  fact  that  undesirable  substances 
are  dissolved  out  while  the  more  de- 
sirable ones  remain  in  the  rubber. 

In  the  case  of  Guayule,  we  are  con- 
fronted by  a  special  proposition.  This, 
coming  as  it  does  from  the  shrubs,  can- 
not be  obtained  by  the  ordinary  means 
of  tapping.  The  process  is  largely  a 
mechanical  one,  but  the  principles  ol' 
peptization  and  pectization  are  both 
taken  advantage  of  in  this  process. 
The  shrubs  are  macerated  in  pebble 
mills  and  then  digested  with  an  alka- 
line solution.  This  pectizes  the  rub- 
ber and  makes  it  possible  to  remove  it. 
After  this  it  is  precipitated.  The  pro- 
cess is  largely  secret. 

Application   of  Colloidal  Chemistry 

Next  in  order  we  shall  discuss  sir 
few  of  the  applications  of  colloidal 
chemistry  to  rubber  manufacture. 

Considering  mixing,  we  must  first 
call  attention  to  the  fact  that  in  break- 
ing down  the  rubber  on  the  mixing 
mills,  we  increase  the  surface.  Inas- 
much as  the  colloidal  action  of  the 
rubber  does  play  a  part  in  its  be- 
havior, the  extent  to  which  we  in- 
crease the  surface  by  this  breaking 
down  process  will  have  a  proportion- 
ate effect  upon  this  action. 

Among  our  compounding  ingredi- 
ents we  have  some  materials  which 
have  high  adsorbtive  power,  others 
which  are  comparatively  inert,  and 
still  others  which  are  more  or  less  ad- 
sorbed. Consequently  we  may  expect 
a  difference  in  the  behavior  of  the 
stock  depending  upon  the  order  in 
which  the  compounding  ingredients 


46 


RUBBER   MANUFACTURE 


are  added.  For  example,  let  us  take 
a  compound  containing  rubber  and 
sulphur,  a  highly  adsorbtive  material, 
and  a  material  capable  of  being  easily 
adsorbed.  If  the  easily  adsorbed 
material  is  one  that  directly  affects 
the  rubber  itself,  the  probabilities  are 
that  it  should  be  added  first  in  order 
that  the  full  extent  of  the  adsorbtive 
forces  between  it  and  the  rubber  may 
be  realized.  If,  on  the  contrary,  the 
highly  adsorbtive  material  has  been 
added  first,  it  would  have  no  doubt 
adsorbed  the  rubber  and  thus  satisfied 
or  at  least  materially  lessened  the  ad- 
sorbtive force  which  the  rubber  pos- 
sessed, 

It  may  be  noted  in  passing  that 
there  are  a  few  materials  which  have 
a  great  influence  upon  the  physical 
properties  of  the  cured  compounds 
where  they  are  used;  and  these  sub- 
stances have  a  high  adsorbtive  power. 
As  the  most  notable  examples  of  this 
phenomenon  we  may  mention  zinc 
oxide  and  lamp  black.  The  latter  is 
one  of  the  best  adsorbents  known  and 
has  the  property  of  increasing  tensile 
strength  of  rubber  compounds  more 
than  any  other  substance.  Without 
exception  the  materials  used  in  rub- 
ber compounding  which  have  slight 
adsorbtive  power  are  practically 
inert  and  serve  merely  as  fillers. 

Of  course  we  must  not  fail  to  re- 
member that  these  materials  which 
we  have  mentioned  which  have  a  great 
absorbtine  power,  likewise  possess  an 
enormous  surface  due  to  their  fine 
state  of  division  and  their  porosity. 
On  the  other  hand,  the  others  are  com- 
paratively coarse  and  more  compact. 

The  theory  has  been  advanced  and 
has  received  considerable  support  that 


the  swelling  of  rubber  in  benzene  may 
be  accounted  for  as  follows:  The 
rubber  possesses  a  more  or  less  cellu- 
lar structure.  Therefore,  when  it  is 
placed  in  benzene,  the  solvent  enters 
these  cells  and  adsorbs  certain  sub- 
stances therein  and  thus  produces 
osmotic  pressure,  which  distends  the 
individual  cells  until  they  burst  open 
and  then  disperse  through  the  solu- 
tion. If  this  theory  is  correct,  it  nat- 
urally follows  that  when  the  solvent 
is  evaporated,  the  residue  should 
possess  different  properties  than  the 
original  rubber.  We  know  that  this 
is  not  true. 

A  much  more  reasonable  explana- 
tion may  be  found  in  our  theory  of 
peptonization  advanced  in  the  last 
chapter.  From  this  we  would  explain 
the  phenomenon  of  rubber  solution  as 
follows : 

When  rubber  is  placed  in  the  sol- 
vent, the  latter  is  adsorbed  by  the  rub- 
ber. The  volume  of  the  solvent  ad- 
sorbed causes  the  swelling  of  the  rub- 
ber until  finally  sufficient  has  been  ad- 
sorbed to  break  up  the  cohesion  be- 
tween the  rubber  particles  and  dis- 
perses it  through  the  entire  solution. 
When  such  a  solution  is  evaporated, 
the  particles  remain  unruptured  and 
will  finally  go  back  to  their  original 
state.  This  is  more  in  accordance 
with  what  actually  happens. 

Furthermore,  if  the  rubber  has  been 
first  broken  down  upon  the  mill,  and 
thus  its  surface  increased,  it  will  ad- 
sorb the  solvent  more  easily  and  give 
a  solution  in  a  shorter  time. 

The  role  of  colloidal  phenomenon, 
as  it  is  applied  to  vulcanization  and 
to  reclaiming  will  be  considered  in  the 
following  chapters. 


CHAPTER  VIII 
Different  Means  of  Coagulation 


While  discussing  the  different  va- 
rieties of  rubber  which  come  from 
the  various  sources,  we  have  called 
attention  in  each  case  to  the  methods 
used  in  their  coagulation.  Some  of 
these  have  been  primitive  and  most 
have  lacked  a  scientific  basis.  The 
result  of  this  has  been  that  some  rub- 
bers from  certain  localities  have  been 
very  good  and  uniform  while  those 
from  other  places  are  characterized 
by  lack  of  uniformity,  and  therefore 
are  expensive  experiments  most  of  the 
time. 

Of  course,  at  present,  the  methods 
of  control  are  more  uniform  on  the 
plantation  and  as  a  result  the  rub- 
ber from  these  sources  is  the  most  uni- 
form found  in  the  market.  That  leads 
us  to  suspect  that  the  wide  variance 
in  native  rubbers  is  occasioned  prin- 
cipally by  the  lack  of  uniform  meth- 
ods of  coagulation.  This  has  led 
men  to  investigate  the  different 
methods  in  use,  with  the  idea  of  try- 
ing to  find  some  more  satisfactory 
process  than  is  at  present  known. 
They  have  been  guided  by  observa- 
tions of  conditions  which  exist  in 
places  from  which  the  various  grades 
are  obtained. 

"We  know  the  rubber  from  the  Ama- 
zon to  be  the  most  uniform  of  any 
wild  rubber  on  the  market.  When 
we  observe  the  methods  by  means  of 
which  the  seringueiro  collects  and 
coagulates  the  latex  from  the  Hevea 
and  thus  obtains  Para  rubber,  we 
eonie  to  the  conclusion  that  the 
process  wherever  and  by  whomever 
used  is  one  that  will  produce  a  uni- 
form product.  On  the  other  hand, 
when  we  observe  the  product  from 
Africa  and  notice  the  great  differ- 
ences even  in  the  same  grades,  we 
are  satisfied  in  our  own  minds  that 
the  methods  used  must  be  at  fault. 


The  whole  trade  recognizes  that  we 
have  not  at  present  any  method  of 
coagulation  that  is  entirely  satisfac- 
tory. This  is  very  apparent  when 
we  realize  that  even  the  method 
which  produces  the  most  uniform 
rubber  of  all,  namely,  the  plantation, 
is  at  present  under  severe  criticism, 
and  chemists  are  employed  to  make 
a  thorough  study  of  this  whole  ques- 
tion in  order  to  substitute  a  better 
one. 

This  study  is  based  upon  certain 
principles  of  colloidal  chemistry  and 
it  is  hoped  that  by  the  aid  of  these 
investigations  we  are  going  to  be  able 
to  bring  forth  something  new  and 
better.  We  know  that  the  stability 
of  latex  from  different  sources  varies, 
and  we  have  come  to  the  conclusion 
that  this  is  due  to  the  different  size 
of  particles  in  the  different  emulsions, 
to  the  electrical  charge,  and  to  the 
presence  of  protective  colloids,  etc. 
Fickendey  (Z.  Chem.  Ind.  Kolloids, 
1911,  8,  43)  calls  attention  to  the  fact 
that  coagulation  in  general  consists 
in  the  removing  of  the  proteins  or 
peptones,  which  serve  as  protective 
colloids,  and  then  the  neutralization 
of  the  electrical  charges.  Upon  the 
addition  of  acid  to  the  latex,  we  ef- 
fect coagulation  in  all  cases  except 
Funtumia.  This  latter  fact  has  been 
explained  upon  the  ground  that  it  is 
a  case  of  a  peptone  acting  as  the 
protective  colloid  instead  of  a  pro- 
tein. However,  Spence  has  shown 
that  the  size  of  the  particle  in  the 
Funtumia  latex  has  a  great  deal  to 
do  with  its  stability  also,  for  he  re- 
moved the  peptone  by  treatment  with 
trypsin  and  no  coagulation  resulted. 
(Quar.  Jour.  Reprints,  1907,  9,  5.) 

The  Brownian  Movements  are  ap- 
parent in  the  latex  and  V.  Henri 
(Le  Caoutchouc  et  la  Gutta  Percha, 


47 


48 


RUBBER   MANUFACTURE 


1908,  5,  2405)  took  advantage  of  this 
to  study  the  effects  of  acids  and 
alkalis  upon  it.  He  found  that  the 
addition  of  acids  greatly  reduced  the 
velocity  of  the  rubber  particles,  while 
alkalis  had  much  less  effect.  When 
the  acid  was  increased,  the  particles 
seemed  to  form  in  a  sort  of  network. 

This  is  interesting  from  a  scientific 
point  of  view,  but  its  influence  upon 
the  manufacture  may  be  slight,  yet 
today  we  are  also  having  it  studied 
from  the  manufacturer's  side. 

It  was  to  study  this  problem  from 
this  angle  that  Eaton  and  Grantham, 
in  the  Department  of  Agriculture  of 
the  Federated  Malay  States,  started 
on  what  might  be  called  the  first 
scientific  investigation  of  this  subject 
of  coagulation  and  its  effect  upon 
the  rubber  obtained  for  manufactur- 
ing purposes. 

The  manufacturer  had  observed 
the  difference,  which  we  find  in  the 
mechanical  curing  of  rubber  from 
different  sources  and  in  fact  from 
the  same  source.  Some  forms  of 
rubber  from  a  certain  plantation  will 
cure  in  a  way  different  from  that  of 
another  variety  from  the  same  place. 

Corresponding  grades  from  different 
plantations  likewise  show  different 
peculiarities  in  curing.  This  of 
course  raised  the  question  as  to  what 
caused  this  variance.  It  led  some 
men  to  think  that  in  order  to  use 
any  rubber  intelligently,  one  must 
know  the  complete  life  history  of  it: 
where  it  came  from,  how  it  was  gath- 
ered, how  it  was  coagulated,  how  it 
was  treated  after  coagulation,  what 
form  it  was  put  into,  how  old  it  was, 
and  many  more  facts. 

In  the  first  experiment  of  Eaton 
and  Grantham,  which  appeared  in 
the  Agricultural  Bulletin  of  the 
F.  M.  S.,  they  call  attention  to  two 
facts. 

(1)  That  in  plantation  rubbers 
there  is  a  great  variation,  but  this 
comes  largely  in  the  rate  of  cure  and 
not  in  mechanical  properties,  since 
similar  mechanical  properties  can  be 
obtained  in  the  vulcanized  material, 
provided  the  correct  rate  of  cure  of 
the  rubber  under  specific  conditions 
is  known. 


(2)  That  this  variation  in  rate  of 
cure  or  vulcanizing  capacity  is  due 
to  some  substance  existing  in  the 
latex,  or  formed  subsequently,  which 
in  the  prepared  raw  rubber  acts  cata- 
litically  as  an  accelerator,  and  that 
the  rate  of  cure  of  raw  rubber  de- 
pends on  the  amount  of  this  substance 
remaining  in  the  raw  rubber,  which 
again  depends  on  the  mode  of  coagu- 
lation and  preparation.  In  trying 
to  establish  these,  they  selected  what 
they  regarded  as  a  set  of  uniform 
conditions  for  determining  what  is- 
known  as  the  "  optimum  cure,"  that 
is,  the  cure  which  shows  the  maxi- 
mum product  of  elongation  by  tensile- 
strength.  They  cured  all  of  their 
samples  at  a  temperature  of  140* 
C.  and  took  test  strips  every  fifteen 
minutes.  The  sulphur  content  was- 
10  per  cent  of  the  whole  mixture. 

The  first  tests  were  made  upon 
Plain  Crepe  and  Smoked  Sheet.  Both 
of  these  showed  the  optimum  cure  at 
three  hours.  At  this  point  they  re- 
ceived a  sample  of  ' '  Byrne  cured' 
slab, ' '  and  when  this  was  tested  out  it 
showed  the  "  optimum  cure  "  at  one- 
hour  and  fifteen  minutes.  Here  we 
have  a  rubber  which  cures  an  hour 
and  forty-five  minutes  more  quickly 
than  plain  or  smoked  sheets,  and  yet 
is  obtained  from  the  same  latex.  You- 
may  immediately  realize  what  this 
means  to  the  manufacturer  of  today. 

Here  two  questions  presented  them- 
selves: (1)  Was  it  due  to  the  Byrne 
fumes,  or  (2)  the  form  in  which  the 
rubber  was  prepared?  They  then 
prepared  what  is  known  as  a  Byrne 
Loaf  (this  is  made  by  rolling  sheets, 
cured  by  the  Byrne  fumes  around  a 
stick,  thus  building  up  a  solid  cylin- 
der of  superimposed  sheets)  ;  this 
rubber  never  completely  dries  in  this; 
form  and  has  to  be  creped  and  dried 
before  vulcanizing.  The  results  on> 
this  loaf,  and  also  upon  pressed  sheet., 
showed  the  optimum  results  at  two- 
hours  and  forty-five  minutes.  This  is, 
practically  the  same  time  as  that  re- 
quired for  plain  crepe  or  smoked' 
sheet,  and  therefore  points  to  the  fact 
that  it  is  not  the  Byrne  fumes  which 
cause  the  variation  in  the  rate  of 
cure. 

A    sample   was   then   prepared   by 


DIFFERENT  MEANS  OF  COAGULATION 


coagulating  the  latex  in  thin  layers 
in  shallow  pans  in  a  smoke  house 
and  thus  superimposing  further  lay- 
ers daily  for  a  period  of  a  week.  By 
this  method  a  slab  of  rubber  result- 
ed, and  when  this  was  cured  and 
tested  it  came  to  the  optimum  test 
in  an  hour  and  a  half.  In  other 
words,  a  rapid  curing  rubber  had 
been  produced,  and  we  are  almost 
safe  in  saying  from  these  two  tests 
that  the  rate  of  cure  is  due  to  the 
form  rather  than  to  the  fumes. 
Further  tests  revealed  the  fact  that 
smoked  sheets  vulcanized  more  slowly 
than  plain  sheets,  and  hence  the  con- 
clusion that  smoking  has  a  tendency 
to  retard  the  rate  of  cure.  We  may 
therefore  call  attention  to  the  follow- 
ing facts: 

(1)  Slab  rubber  smoked  by  Byrne 
fumes     or     rubber     coagulation     by 
smoke,    by   superimposing  layers   of 
latex,  cures  much  more  rapidly  than 
plain  crepe  or  smoked  sheet. 

(2)  Unsmoked    sheet    cures    more 
rapidly  than  smoked  sheet  or  plain 
crepe. 

Latex  was  next  placed  in  a  large 
wooden  box  with  movable  partitions. 
so  that  all  might  receive  the  same 
treatment  during  coagulation;  then 
from  the  coagulum  the  following 
samples  were  prepared : 

(a)  Smoked  sheet,  which  showed 
its  "  optimum  cure  "  in  two  hours 
and  forty-five  minutes. 

(&)  Smoked  sheet,  creped  when 
dry ;  this  required  two  hours  and 
forty-five  minutes. 

(c)  Smoked  slab,  "optimum  cure," 
one  hour  and  forty-five  minutes. 

(d}  Unsmoked  sheet,  "  optimum 
cure,"  two  hours  and  forty-five 
minutes. 

(e)  Unsmoked  sheet,  creped  after 
drying,  "  optimum  cure,"  two  hours 
and  forty-five  minutes. 

(/)  Unsmoked  slab,  "  optimum 
cure,"  one  hour. 

The  conclusions  to  be  drawn  from 
these  tests  are  that  creping  of  dry 
sheet  has  no  effect  upon  rate  of  vul- 
canization ;  also,  that  slab  is  the 
most  rapid  curing  form  of  rubber; 
and  lastly,  that  smoking  will  retard 
the  rate  of  cure  on  slab.  To  explain 


this   behavior,    two   theories   present 
themselves : 

(1)  That    the    latex    contains,    in 
addition  to  the  caoutchouc,  some  con- 
stituents which  influence  the  rate  of 
cure   of   the   rubber,    this   substance 
not    being    precipitated    by     ordin- 
ary coagulation.     Consequently,  the 
greater  the  quantity  of  serum  remain- 
ing in  the  rubber,  the  greater  will  be 
the  quantity  of  this  substance  present 
in  the   raw  rubber.     If  this  is  the 
case,  the  effect  of  smoking  is  appar- 
ently   the    destruction    of    this    sub- 
stance. 

(2)  It  may  be,  however,  that  this 
substance  does  not  exist  in  the  latex, 
but  is  formed  from  some  constituent 
of  the  latter.    In  this  case  the  reten- 
tion of  the  serum  in  the  rubber  would 
appear   to   encourage   the   formation 
of  the  catalytic  substance.     Our  or- 
dinary methods  of  analysis  of  crude 
rubber,  of  course,  will  not  reveal  the 
presence    of   these   substances.      For 
instance,  we  determine  the  nitrogen 
in  the  rubber  and  calculate  it  all  a& 
proteins  and  this  may  be  far  from 
the  actual  truth  of  the  way  the  nitro- 
gen really  does  exist.     We  do  know 
that  certain  amines  have  an  accelerat- 
ing  effect   upon   vulcanization,    and 
it  follows  that  perhaps  some  of  these 
proteins  do   decompose  into  amines, 
and  therefore  the  greater  the  amount 
of    serum    left    in    the    rubber,    the 
greater     will     be     this     effect.       Ta 
strengthen    this    theory,    Eaton    and1 
Grantham  observed  that  we  get  slow 
curing   rubbers    from    latex    treated 
with  preservatives,  or  from  smoked 
rubbers,  which  act  in  the  same  way. 
Jf  this  change  is  caused  by  an  enzymer 

then  the  same  may  be  expected  for 
the  preservative,  or  smoke  would  of 
course  kill  it  and  thus  produce  a  slow- 
vulcanizing  rubber. 

That  this  material  is  present  in  the 
latex  is  also  substantiated  by  the  fact 
that  synthetic  rubber  is  very  difficult 
to  vulcanize. 

Another  fact  pointing  in  the  same 
direction  is  that  air-dried  slab  is  the- 
most  rapid  curing  and  also  has  the 
most  serum  remaining  in  the  rubber. 

Fine  hard  Para  is  rather  slow  cur- 
ing, due  to  the  fact  that  the  smoke- 
in  coagulating  has  its  maximum  ef- 


50 


RUBBER  MANUFACTURE 


TABLE  I 
Latex,  Acetic  Acid  Coagulated 


Sheets 

I 


Smoked 

Creped 
1M  hrs. 

Una 
Air 

Cre 

1 

moked                                       Sm 
dried 

ped 

IT. 

aked                                                 Unsmoked 
Air  dried 

1 

plain              creped 
L):i4  hrs.          2M  hrs. 

plain                                            creped 
2%  hrs.                                           2?4  hrs. 

TIME  REQUIRED  FOB  CURING  VARIOUS  KINDS  OF  RUBBER. 


feet.  The  ' '  optimum  cure  ' '  requires 
from  two  and  one-half  to  two  and 
three-quarters  hours. 

The  rate  of  cure  of  samples  from 
different  states  shows  quite  a  vari- 
ance due  to  many  causes,  e.  g.,  dilu- 
tion of  latex,  working  of  rubber, 
thickness  of  rubber,  smoking,  rapid- 
ity of  drying,  amount  of  coagulant, 
etc.  (Agricultural  Bulletin,  Feder- 
ated Malay  States,  March,  1915.) 

The  lack  of  uniformity  in  these 
rubbers  is  of  great  importance  to  the 
manufacturer,  for  if  by  regulating 
the  preparation  of  the  rubber  from 
the  latex  we  are  able  to  procure  a 
rapid  curing  rubber,  then  a  great 
deal  of  cost  in  the  manufacture  is 
saved  and  a  greater  output  is  also 
made  possible  with  the  same  equip- 
ment and  number  of  men. 

Eaton  and  Grantham  have  also 
conducted  experiments  to  find  the  ex- 
tent to  which  lack  of  uniformity  in 
the  mechanical  method  of  procedure 
in  the  preparation  of  rubber  from  the 
latex  caused  variation  in  the  product. 
(Agricultural  Bulletin,  Federated 
Malay  States,  111,  218,  1915,  et  seq.) 
They  found : 

(1)  That  after  the  rubber  has  once 
been  reduced  to  a  thin  sheet,  exces- 
sive creping  has  little  or  no  effect. 

These  conclusions  were  based  upon 
the  results  obtained  from  passing 
different  lots  of  the  same  rubber 
through  the  creping  machine  five,  ten. 
fifteen,  twenty,  and  twenty-five  times, 
respectively.  Excessive  maceration, 
however,  does  seem  to  have  a  slightly 
retarding  effect  upon  the  rate  of  cure. 


An  interesting  feature  of  the  experi- 
ment was  shown  by  repeating  the 
tests  on  mixtures  out  of  these 
samples,  made  eight  months  later. 
These  tests  indicated  somewhat 
slower  cure  in  the  sample  creped 
twenty-five  times.  This  is  particularly 
interesting  because  of  the  apparent 
recovery,  which  has  been  so  com- 
monly noticed  after  rubber  broken 
down  on  the  mills  has  been  allowed 
to  stand. 

(2)  That  the  use  of  more  acid  than 
necessary  to  produce  coagulation  has 
the   effect   of   slightly  retarding   the 
cure.     The  use  of  sodium  bisulphite 
has  no  effect. 

(3)  That  samples  of  rubber  from 
the  same  latex  were  taken  at  different 
stages  in  the  preparation  as  follows: 
a,    Coagulated   slab   and   allowed   to. 
drain;  b,  after  rolling  once;  c,  rough 
crepe;  d,  thick  crepe;  e,  thin  crepe. 

These  samples  were  kept  for  twenty 
days ;  then  samples  A,  B  and  C  were 
made  into  thin  crepe  and  all  five 
samples  were  dried,  after  which  they 
were  compounded  similarly  and 
cured.  The  "  optimum  cures  "  re- 
ported were :  a,  1  hr.,  30  min. ;  &,  2 
hr. ;  c,  2  hr.,  30  min.;  d,  2  hr.,  45 
min. ;  e,  3  hr.,  thus  substantiating 
their  contention  that  each  step  of  the 
process  seems  to  have  a  retarding  in- 
fluence on  the  cure. 

Continuing  on  this  line,  they  went 
further  into  the  effect  of  drying  in 
hot  air  driers  up  to  2  hr.,  at  150 
deg.  F.,  samples  being  taken  prac- 
tically as  before  and  also  a  sample 
being  taken  from  the  drier  every 


DIFFERENT  MEANS  OF  COAGULATION 


51 


best  advantages.     Their  data  may  be 
summarized  as  follows : 


hour.      All    of    the    samples,    which 

had   been    in   the   drier   required    3 

hr,  15  min.  for  curing  or  15  min.  T      of  Rubber  Nj          Cure 

more  than  the  time  required  for  thin  Smoked  sheets 0.445  per  cent   3  hr. 

Smoked  sheets  after  ereping. . .   0.441  per  cent     3  hr. 

Crepe.  Smoked  slab  after  ereping 0.451  per  cent     1M  hr. 

Unsmoked  sheet 0.423  per  cent     2%  hr. 

(4)     That  tests  Of  the  product  from  Unsmoked  sheet  after  ereping. .   0.434  per  cent     2%  hr. 

i          ji     i       r.  Unsmoked  slab  after  ereping....  0.321  percent 

the    estate    handled    by    the     same  Thick  smoked  slab 0.425  per  cent 

mo-rlmrJc     AVOVP     rmi+P     nnifnrm          Onp  Thin  smoked  slab 0.398  per  cent 

memOaS     \\ere     quite  m.  Thick  smoked  sheet 0.400  percent 

interesting      thing      was      indicated  Thin  smoked  sheet.. o.4ie  per  cent 

„  , ,  Thick  unsmoked  slab 0.210percent     IX  hr. 

through  the  COUrse  01  these  teStS.      Un  Thin  unsmoked  slab 0.352  per  cent     l^hr. 

•Hx-rv      rvrtnoeirvnc      +Vio      tr-ooc      worp      r>pr  Thick  unsmoked  sheet 0.386  per  cent     2*^  hr. 

t^O      OCCaSlOnS      tile      trees      Were     pe.  Thin  unsmoked  sheet 0.394  percent     Shr. 

mitted    tO    rest    longer    than    USUal    be-  Unsmoked  slab  dried  externally, 
„          .         „                     i      i        ji  results  calculated  on  82.  /  per 

CailSe     Of    ram     tor    a     WhOle    day;     On  cent  dry  rubber 0.307  per  cent 

_ji  ji         A  „    I_A_         'PUr,  Sliced  slab  heated  to  100  deg. 

another  the  tapping  was  late.      1  he  c  till  drv »;  0  240  per  cent 

quality     of    rubber     obtained     from  Dry  crepe  from  slab  (dried 

*    ,  .  without  heating) 0.218  per  cent 

these  subsequent  tappings  was  above 

the  average.  Results  on  the  following  data  cal- 

culated on  the  basis  of  the  dry  rubber 

(£>)  That  the  following  experiments  present- 
indicated  the   effects  of  leaving  the 

COaglllatum  in  Slab  form  for  ten  daYS  Wet  slab  2  hr.  after  pressing...   O.GOO  percent      . 

0  .  Wet  slab  alter  drying  thirteen 

before  Curing  :  days 0.324  per  cent 

.  .  Dry  crepe  from  slab 0.220  per  cent 

a    Block    prepared    as    USUal    On    the  Wet  crepe   made  immediately 

day  following  coagulation,  cured  in  Ab^cre^whendry. '.'.::::;  aleo  per  cent 

3  hr.,  15  min.  ,,T  .      ,,       , 

.       .  We  may  summarize  the  above  data 

6  Block     prepared     after    leaving  in  ^  followi       conclusions: 
coagulum  from  some  of  the  same  latex  •,•,•,,         * 

in  the  slab  form  ten  davs  before  crep-  (D  *****  smoke(*  rubbers  ff^ 

ing,  blocking  and   drying,   cured   in  the  sanie  J^x  the  nitrogen  content 

1  hr    15  min  1S  constant,  although  the  rate  of  vul- 
canization    varies     considerably    be- 

c  Slab,   prepared  the  same   as  B,  tween  siajj  an(j  s]ieet     Smoking  ap- 

cured  in  1  hr.,  15  min.  pears  to  fix  the  nitrogen. 

Sodium   bisulphite    had   no   effect  (2)   Among      unsmoked      rubbers 

when   used   in   parallel   experiments.  from  the  same  latex  there  is  a  con- 

The  mechanical  qualities  of  a  Avere  siderable    variation    in    the   nitrogen 

<i]so  inferior.  content  of  the  rubber  after  ereping 

By  mixing  proportionate  amounts  preparatory     to     the     vulcanization 

of  fast  and  slow  curing  rubbers  to-  process.     It  is  small  in  the  case  of 

gether,  the  rate  of  cure  may  be  ad-  rapidly     vulcanizing     rubbers     and 

justed  to  uniformity.     They  explain  larger  in  the  case  of  the  more  slowly 

the  uniformity  of  fine  hard  Para  by  vulcanizing  ones, 
the  fact  that  a  single  ball  represents  (3)  The  low  percentage  of  nitrogen 

latex  collected  day  after  day  for  a  in  rubber  prepared  as  unsmoked  slab 

period  of  months.     In  passing,  it  is  is    attributed   partly    to   loss    in   the 

but   fitting  to  note   that  many  com-  gaseous   form  during  the  superficial 

pounders  prefer  to  use  a  mixture  of  drying  of  the  slab,  and  partly  to  the 

rubbers  in  their  stocks  so  that  the  washing   out  of  nitrogenous  decom- 

variation  in  different  lots  of  each  may  position  products  Avhen   the   slab   is 

be    averaged    and    a    more    uniform  creped  prior  to  vulcanization, 
product  obtained.  (4)      gmce     rapidly     vulcanizing 

An  attempt  has  also  been  made  smoked  slab  rubber  contains  as  high 
(Agricultural  Bulletin,  Federated  percentage  of  nitrogen  as  slowly  vul- 
Malay  States,  IV,  1,  1915)  under  canizing  sheets,  the  actual  loss  _of 
the  direction  of  Mr.  Eaton  to  deter-  nitrogen  cannot  be  the  cause  of  rapid- 
mine  the  influence  of  the  nitrogen  ity  of  vulcanization,  although  it 
content  on  the  cure  with  the  possible  would  appear  from  the  results  of  the 
view  of  regulating  this  factor  to  the  unsmoked  rubbers  that  rapidity  of 


52 


RUBBER    MANUFACTURE 


vulcanization  and  loss  of  nitrogen  are 
in  some  way  associated. 

Eaton  and  Day  (Agricultural  Bul- 
letin, Federated  Malay  States  IV,  350, 
1916)  have  followed  the  change  of 
the  nitrogen  content  through  the  dif- 
ferent stages  of  handling  the  latex. 
The  results  are  summarized  in  the 
accompanying  chart.  (Table  II.) 

The  same  coagulum,  converted 
directly  to  sheet  and  crepe,  on  the 
day  following  coagulation  contained 
0.40  per  cent  nitrogen,  or  about  twice 
as  much  as  the  other. 

In  1912  Whitby  presented  before 
the  Congress  of  Applied  Chemistry, 
a  paper  in  which  he  made  the  claim 
.that  the  natural  coagulation  of  Hevea 
latex  was  brought  about  by  a  coagu- 
lating enzyme. 

Eaton  and  Grantham  carried  out 
a  series  of  experiments  along  this 
line  and  came  to  the  following  con- 


latex  under  anaerobic  conditions  is; 
not  constant,  on  some  days  complete 
coagulation  occurring  and  on  others 
much  less  complete.  This  is  possibly 
due  to  a  variation  in  the  constituents- 
of  the  latex. 

(4)  That  by  the  addition  of  various 
sugars,  coagulation  under  both  con- 
ditions always  occurs  and  is  due  in 
their  opinion  to  the  fact  that  a 
medium  is  formed  more  favorable  for 
the  organisms,  which  produce  coagu- 
lation, and  less  favorable  to  those 
producing  putrefactive  changes. 

In  a  previous  article  by  these  me» 
they  called  attention  to  the  fact  that 
an  excess  of  acetic  acid  in  coagula- 
tion retards  the  rate  of  cure  arid  upon: 
biological  grounds  it  is  explained  that 
the  micro-organisms  which  produce 
accelerating  substances  are  killed.  To- 
investigate  this  point,  some  rubber 
was  coagulated  with  acid  and  then 


TABLE  II 
Latex.     (N2  content  0.1.1%) 


Wet  coagulum  67  parts,  by  weight, 
Ns  0.15% 

Pressed 


Wet  coagulum  remaining  50 
parts  N2  0.26%  which  is 
equivalent  to  0.78%  N«  on 
dry  rubber  present. 

Hand  rolled  after  standing 
six  weeks  to  19.1  parts  con- 
taining 0.20%  N2  or  an 
equivalent  of  0.23%  N*  on 
the  dry  rubber  present. 

Washed,  creped  and  dried 
gave  16.4  parts  of  dry  rubber 
containing  0.19%  Nj;  the 
loss  here  was  probably  me- 
chanical due  to  the  removal 
of  the  surface  scale  which 
had  formed  and  which  was 
high  in  proteins. 


Serum  pressed  out  17 
parts— S.  G.  1.011 
N2  0.07% 


Serum  33  parts  (S.  O.  1.009) 
N2  0.06% 

Held  for  14  days  with  no 
evaporation  Nz  0.04% 

Held  for  60  days  with  no 
evaporation  Nj  0.03% 

Mo  further  loss  in  Ni. 


elusions  (Agricultural  Bulletin,  Fed- 
erated Malay  States,  Nov.,  1915)  : 

(1)  That  this  natural  coagulation 
of  the  latex  of  Hevea  braziliensis  is 
due  to  certain  bacteria  which  infect 
the  latex  after  coagulation. 

(2)  That   these   are   two   distinct 
types  of  organisms,  one  favored  by 
aerobic  conditions,  which  tend  to  in- 
hibit    coagulation,     and     the     other 
favored     by     anaerobic     conditions, 
which  affect  coagulation  of  the  latex. 

(3)  That  the   coagulation   of  the 


soaked  in  alkaline  solutions,  thus  pro- 
ducing a  more  favorable  medium  for 
biological  changes  to  occur.  Slab 
rubber  was  the  form  chosen  with 
which  to  carry  out  the  test.  The  re- 
sults were  that  the  rubber  cured  in 
about  one  half  the  normal  time. 
Whether  this  is  to  be  explained  upon 
purely  a  chemical  or  biological  basis- 
remains  for  further  research,  which 
has  been  attempted  at  a  more  recent 
date. 

If  the  preceding  assumptions  are 


DIFFERENT  MEANS  OF  COAGULATION 


53 


•correct  that  there  exists  in  the  rubber 
some  substance  which  has  the  power 
-of  decomposing  into  accelerating 
•compounds,  the  question  arises,  What 
is  the  period  during  which  the  change 
in  the  ra\v  rubber  causing  accelera- 
tion of  rate  of  cure  takes  place? 

To  answer  this  question,  the  two 
•experimenters,  above  referred  to, 
coagulated  some  latex,  then  from  the 
coagulum  removed  a  sample  creped. 
•dried  it  in  a  hot  air  drier  and 
then  blocked  it  on  the  same  day 
as  coagulated.  The  next  day  a  new 
sample  was  taken  from  the  original 
coagulum  and  treated  in  the  same 
manner;  the  following  day  another 
sample,  and  so  on  until  they  had  ten 
-samples  taken  in  as  many  days.  These 
•were  then  milled  up  and  cured, 


ber  after  the  tenth  day  and  it  will 
remain  constant  after  that  time. 
Even  samples  that  have  been  aged 
seem  to  retain  their  accelerating 
bodies. 

In  the  above,  attention  was  called 
to  the  remarkable  accelerating  action 
which  alkalis  have  upon  rate  of  cure 
and  it  was  suggested  that  this  might 
be  due  either  to  a  biological  effect 
or  to  a  purely  chemical  one.  Eaton 
investigated  this  point  in  the  follow- 
ing manner: 

Samples  of  both  fast  curing  and 
slow  curing  rubbers  were  taken  arid 
soaked  in  dilute  alkaline  and  acid 
solutions  for  twenty-four  hours,  then 
milled,  cured  and  tested,  comparison 
being  made  in  each  case  against  a 
control  sample. 


TABLE  III 


Not  coagulated.  Evap- 
orated rapidly  over  CaCls 
to  avoid  decomposition 
^nd  retain  all  the  serum. 

•Gave  very  fast  cure  rub- 
iber. 


Latex 
Water 
Protein 
Carbohydrates 
Resins 
Mineral  Matter 
Rubber 

1 

Aerobic  Fermentation. 

Proteins  putrefy 
Rubber  liquefies. 

Coagulated 

Aoetio  acid 

by     •             Anaerobic  Fermentation. 

Non-putrefactive. 
Amido  compounds 
formed  which  acceler- 
ated  cure.     The   rubber 
sometimes     coagulates 
spontaneously  and  is  al- 
ways   coaguable   by    the 
usual  methods. 


Xoncoaguable. 
Hastens  cure  if  used 
with   coaguable  rubber. 


1 

1 
Serum 

Evaporated  bv  heat 

1 

Rubber 

Left  with  some- 
moisture  in 
-shipping.  Aero- 
bic.   Fast  cure. 
Byrne  process  .Slab 
rolled  up  and 
smoked  while 
drying.    Anaerobic. 
Fast  cure 

E.  &  G.  method 
of  allowing  moist 
slabs  to  stand  G 
days.   Anaerobic. 
Fast  euro. 

1 

Protein  precipitated 
by  heat 

Proteins  decom- 
posed anaerobic- 
ally  has  marked 
accelerating 

I'ndecomposed 
portion  has  no 
accelerating 
action 

action  on  slow 
cure  rubber. 

Residue  after  removing  insoluble  protein  evaporated 
to  sticky  deliquescent  mass  and  desiccated  in  vacuo. 
Has  decided  accelerating  action  on  slow  cure  rubber 
and  is  stable  to  putrefactive  organisms.  Not  deter- 
mined whether  nitrogenous  or  not. 


tested,  and  the  following  conclusions 
were  drawn : 

(1)  That  the  rate  of  cure  increases 
until  the  sixth  day  and  then  remains 
practically  constant. 

(2)  That  the  greatest  change  occurs 
in  the  first  three   days.     It  is  per- 
fectly safe,  however,  to  crepe  the  rub- 


It  was  found  that  the  alkalis  had 
a  marked  accelerating  action  upon 
the  rate  of  cure,  which  was  apparent 
in  both  the  fast  and  slow  curing  rub- 
bers, while  acid  had  a  pronounced 
retarding  effect.  These  tests  were 
carried  out  with  finished  dried  crepes 
so  that  the  biological  effect  was  elim- 


54 


RUBBER   MANUFACTURE 


mated  and  thus  the  chemical  action 
made  more  certain.  However,  the 
way  in  which  this  chemical  effect 
takes  place  is  not  known.  The  evi- 
dence seems  to  point  to  the  action  of 
the  alkali  upon  certain  constituents 
in  the  rubber.  The  retarding  effect 
of  mineral  acids  is  especially  noted 
with  quantities  beyond  the  minimum 
required  for  coagulation;  therefore, 
the  serious  question  of  trying  to  sub- 


stitute sulphuric  acid  in  the  place  of 
acetic  as  now  used. 

Attention  has  also  been  called  to- 
the  fact  that  rubbers  which  have  been 
treated  with  alkalis  do  not  show  good 
tests  upon  ageing. 

Let  us  hope  that  more  work  along 
this  line  will  follow  and  that  better 
methods  of  coagulation  will  be  found, 
thus  producing  more  uniform  rub- 
ber from  the  manufacturer's  view- 
point. 


CHAPTER  IX 
Theory  of  the  Constitution  of  Rubber 


To  determine  the  true  constitution 
of  caoutchouc  is  no  easy  matter,  as 
will  be  seen  from  what  follows.  In 
the  first  place,  we  must  be  certain 
that  we  have  obtained  a  pure  sample 
with  which  to  work.  The  fact  that 
it  belongs  in  that  class  of  compounds 
which  occur  in  the  realm  of  colloidal 
chemistry  does  not  simplify  our  task 
to  any  great  extent. 

It  has  no  definite  melting  point,  no 
solution  from  which  it  may  be  crys- 
tallized. Ozone  does  form  with 
caoutchouc  an  ozonide  which  is  cap- 
able of  being  purified  and  studied. 
It  was  by  means  of  this  that  Harries 
came  to  the  conclusion  that  there 
existed  a  slight  chemical  difference 
in  the  constitution  of  Congo  caout- 
chouc and  Para.  (Annalen,  1913,  395, 
211.)  For  some  time  caoutchouc  has 
been  given  the  formula  of  C5  H8  and 
then  on  account  of  its  analogy  to  the 
terpenes  it  is  written  C10  H1G  or  some 
multiple  of  this.  Faraday  and  Ber- 
zelius  were  in  possession  of  this 
knowledge. 

The  first  important  Avork  along 
this  line  was  done  by  Gladstone  and 
Hibbert.  (Trans.  Chem.  Soc.,  1888. 
53,  679.)  They  tried  to  obtain  pure 
rubber  by  dissolving  it  in  chloroform 
and  then  precipitating  it  with  alco- 
hol. Even  this  method  seems  to  give 
a  sample  which  contains  some  oxygen. 

They  found  upon  analysis  of  a  sam- 
ple prepared  as  stated  above  that  it 
contained  C  —  87.46  and  H  =  12.00. 
They  calculated  upon  the  basis  of  C  = 
88.24  and  H=  11.7  the  formula  C5HS. 

We  are  fortunate,  however,  in  hav- 
ing more  evidence  as  to  its  formula 
than  that  of  analysis  alone.  The 
usual  methods  of  determining  molecu- 
lar weights,  of  course,  cannot  be  ap- 
plied here,  colloidal  solutions  showing 


very  little  if  any  osmotic  pressure 
and  not  obeying  the  freezing  point 
and  boiling  point  lawTs  of  Roult. 

Bary  and  Weidert  (Compt.  Rend. 
1912,  154,  1159)  assumed  that  the 
molecule  of  caoutchouc  was  made  up 
of  several  nuclei  of  five  or  ten  carbon 
atoms  each.  Then  they  tried  to  ex- 
plain that  the  vulcanization  consisted 
in  the  union  of  an  atom  of  sulphur  to 
each  end  of  a  chain  of  C10Hlf,  com- 
plexes. 

If  this  is  true,  then  the  (C10H16)n 
has  a  value  of  nearly  2500,  which 
makes  the  molecule  appear  to  be  a 
very  large  one.  It  is  also  apparent 
that  if  we  continue  to  vulcanize  and 
go  on  toward  ebonite,  before  that  is 
possible,  there  must  be  a  breaking 
down  of  this  large  molecule  that  more 
sulphur  may  add  itself;  or,  in  other 
words,  depolymerization  must  take 
place. 

It  does  not  seem  necessary  to  hold 
that  the  caoutchouc  molecule  is  a 
large  one.  We  have  two  derivatives 
whose  molecular  weights  have  been 
determined,  the  ozonide  and  nitro- 
sites,  and  these  point  to  a  carbon 
content  of  ten  and  twenty  atoms. 

Some  day  we  hope  to  find  a  solvent 
which  will  resolve  the  colloidal  ag- 
gregation of  a  rubber  solution  into 
a  true  solution  and  thus  make  the 
direct  determination  of  its  molecular 
weight  possible. 

We  know  that  by  certain  manipu- 
lations we  are  able  to  change  the 
aggregations  in  colloids  and  thus  pro- 
duce substances  of  different  proper- 
ties. This  Harries  did  in  the  case  of 
caoutchouc  (Annalen,  1911,  383.  157) 
and  he  obtained  three  materials  which 
lie  designated  as  a,  6  and  c. 

The  a  material  is  obtained  by  pre- 
cipitation with  alcohol.  The  b  is  in- 


55 


56 


RUBBER   MANUFACTURE 


soluble  and  is  formed  when  a  is  al- 
lowed to  stand.     The  c  is  an  oil  ob- 
tained from  a  by  maintaining  a  tem- 
perature  a  little   above  normal.     It 
has   been   suggested   that   the   caout- 
chouc  exists    in    the   latex   in   the   c 
modification     which     is     soluble     in 
ether.     Harries  extracted  some  from 
the  latex  with  ether  and,  upon  stand- 
ing,  this  changed  over  into   rubber. 
Weber   had    observed   this    and    put 
forth    the   idea   that   this    substance 
was  a  dipentene  C20IL!2  in  the  latex 
surrounded  by  a  protein  which  acted 
as   a   protective   colloid.      Therefore, 
when  the  coagulation  reagent  is  add- 
ed, this  protein  is  removed  and  at  the 
same    time    the    dipentene    is    poly- 
merized, for    it    becomes    insoluble. 
Henrichsen     and     Kindscher     (Ber. 
1909,     42,     4329)     determined     the 
molecular  weight  of  the  hydrocarbon 
from  the  latex  by  extracting  it  with 
benzine  and  determining  the  lowering 
of  its  freezing  point.     This  gave  a 
molecular  weight  of  over  3000,  and 
they    felt    certain    that    the    rubber 
existed  in  a  colloidal  state  and  that 
it  was   not   a   dipentene.     In    1860, 
Greville     Williams     distilled     some 
rubber  at  as  low  a  temperature  as 
possible  and,  upon  refractioning,  ob- 
tained    two     samples     with     boiling 
points  between  37-40  degs.  and  170- 
180    degs.,    respectively.      The    first 
portion  was  mostly  isoprene  and  the 
latter     was     caoutchine,     possessing 
twice  the  vapor  density  of  isoprene. 
Boiichardat  (Compt.  rend.,  1879,  89. 
361   and   1117)    found  that  isoprene 
changed,  when  allowed  to  remain  in  a 
sealed   tube,   to   a   substance   having 
a     different    odor.       Then     Wallach 
(Annalen,  1884,  255,  311;  1885,  227, 
292;  1887,  238,  88)  pointed  out  that 
this    substance    was    identical    with 
caoutchine  and  dipentene.     Then  Til- 
den  found  that  dipentene  decomposes 
into  isoprene  and  this  has  been  found 
by  Wallach  to  change  into  caoutchouc. 

Thus  we  may  get  the  relations  of 
these  substances  as  follows:  Caout- 
chouc by  heat  changes  into  isoprene 
and  dipentene;  dipentene  in  a  red 
hot  tube  changes  to  isoprene  ;  isoprene 
spontaneously  changes  into  caout- 
chouc :  in  a  sealed  tube,  however, 
isoprene  goes  into  dipentene.  Other 


fractions  have  been  obtained  and 
studied,  but  few  conclusions  have 
been  drawn  from  that  source. 

We  know  that  caoutchouc  is  an 
unsaturated  hydrocarbon,  but  the  ex- 
act degree  of  this  unsaturation  has 
been  a  subject  of  dispute.  For 
instance,  Gladstone  and  Hibbard 
(Trans.  Chem.  Soc.,  1885,  53,  679) 
described  a  chloride  of  the  formula 
C10H14C1S,  which  is  best  explained 
by  assuming  the  addition  of  six  atoms 
of  chlorine  thus  indicating  these 
ethylene  groups. 

Harries  then  tried  the  action  of 
ozone  upon  a  chloroform  solution  of 
purified  Para  rubber  and  obtained  a 
compound  giving  a  molecular  weight 
according  to  the  formula  C10ITir)00. 
By  a  previous  experiment,  it  was 
found  that  in  ozonides  we  have  three 
atoms  of  oxygen  associated  with  each 
ethylene  group,  therefore  we  must 
have  here  two  such  linkages  for 
each  ten  carbon  atoms.  Harries  also 
produced  a  diozonide  of  the  formula 
C10H1GOS.  When  this  was  hydrolyzed 
there  resulted  hydrogen  peroxide,  a 
keto-  or  di-aldehyde,  laevulinic  acid, 
and  also  another  acid.  To  explain 
this,  he  assumed  that  the  caoutchouc 
molecule  may  be  represented  by  an 
open  chain  formula.  He  later  found 
that  this  was  not  true,  but  that  the 
primary  products  of  hydrolysis  were 
laavulinic  aldehyde  and  the  peroxide 
of  laevulinic  aldehyde : 


O 


(CH3) 


CH.      CH 


'0 


Further  hydrolysis  of  this  decom- 
poses it  into  iasvulinic  acid  and  hydro- 
gen peroxide. 

To  account  for  these  two  primary 
products  of  hydrolysis  from  the 
diozonide  and  the  presence  of  two 
double  bonds  to  each  ten  carbon  atoms 
requires  that  the  molecule  be  re- 
garded as  a  cyclic  one.  because  if  it 
were  an  open  chain  it  would  give  two 
hydrolysis  products  oxygenated  at 
only  one  end  of  their  chains. 

Thus  Harries  suggested  that  the 
constitution  of  caoutchouc  was  repre- 


THEORY  OF  THE  CONSTITUTION  OF  RUBBER 


57 


scnted    by    the    formula    of    a    1  :5 
dimethylclyclooctadiene : 

CH3   •    C   •   CH2    CH2   •   CH 


CH   CH2  •  CH2  •     C 


CH 


Its  ozonide  is  then  : 


o      •  o 

Its  aldehyde  peroxide : 

0 O  0 0 


HC— CH,     .     CH2C-CH3 


CHQ 


CH2     •     CH 


O"  0 

0  O 

0.  -O 


"CH      •      CH2         CH2       C   •  CH3 

Its  aldehyde: 
CH3      C     '•      CHg      CH2         C      -      ft 


CHr 


CH(CHJ, 


Here  Harries  suggested  that  poly- 
merization took  place  due  to  unsatis- 
fied partial  valences  which,  accord- 
ing to  Thiele's  theory,  is  possible 
where  we  have  double  bonds  in  octa- 
diene  ring  formation,  and  thus  an  in- 
definite number  might  be  linked  to- 
gether. 

Pickles  (Trans.  Chem.  Soc.  1910, 
97,  1085)  criticises  this  theory  by  call- 
ing attention  to  the  fact  that  if  this 
were  true,  the  new  polymeride  should 
possess  a  less  degree  of  unsaturation 
than  the  simple  substance,  and  this  is 
not  the  case.  The  tetrabromide  is 
also  formed  without  any  depolymeri- 
zation  and  yet  we  have  four  bromine 
atoms  to  each  ten  carbon  atoms. 

He  also  points  out  that  under*  de- 
structive distillation,  we  should  ex- 
pect to  get  dimethylclyclooctadiene 
and  this  is  not  the  case;  and  yet 
even  under  reduced  pressure  we  never 
get  a  substance  containing  less  than 
twenty  carbon  atoms.  Pickles  chose 
to  assign  a  chain  formula  made  up 
of  C3H8  nuclei : 

CH0 


2'2 


CH(CH2)2     •    C      :      CH    •    CH2 


From  the  study  of  its  oxidation 
products,  we  see  that  the  ends  of  this 
chain  must  be  linked  together.  How- 
ever, the  greater  amount  of  favor 
rests  on  the  side  of  the  eight  mem- 
bered  ring.  Willstatter  (Ber.,  1905. 
38,  1975)  was  able  to  prepare  clyclo- 
octadiene  and  this  he  was  able  to 
polymerize  to  form  diclyclooctadiene : 


CHa CH2 CH 


CH 


CH 


CH CH2 CH2 

If  isoprene  may  be  made  to  con- 
dense and  form  dimethylclyclooc- 
tadiene : 


CH., 


CHn 


CH 


CH 


CH— CK, 


CH., 


CHU 


58 


RUBBER   MANUFACTURE 


Showing  it  in  ring  form : 
Hn 


C  —  CHC 


\ 


H 


then  it  follows  that  butadiene  should 
yield  clyclooctadiene : 

CH=CH2          CH2=CH 


When  Harries  compared  the  ozon- 
ides  of  butadiene,  caoutchouc  and 
clyclooctadiene  when  hydrolyzed,  he 
found  them  to  yield  the  same  prod- 
ucts. This  furnishes  us  the  evidence 
that  caoutchouc  is  an  eight  membered 
ring,  and  from  what  has  been  said 
above  it  does  not  seem  necessary  to 
assume  that  the  molecule  is  any 
larger  than  C10H16. 

When  the  ozonides  of  purified  Para 
and  of  artificial  isoprene  caoutchoucs 
are  hydrolyzed,  they  yield  the  same 
products  and  thus  the  conclusion  that 
the  wild  caoutchouc  must  have  the 
constitution  of  the  polymerized  iso- 
prene. 


CH- 


CHn 


•CH 


\ 


CH 


CH 


CH 


CH 


CH 


CH0 


CHAPTER  X 
Synthetic  Caoutchouc 


The  question  of  being  able  to  pro- 
duce artificial  rubber  is  one  that  has 
interested  a  great  many  workmen 
and  especially  has  it  been  of  great 
interest  to  the  laymen  of  the  rubber 
industry.  I  once  heard  the  superin- 
tendent of  a  large  rubber  factory  say, 
when  asked  his  opinion  as  to  the  pos- 
sibility of  synthetic  rubber,  that  he 
expected  to  see  "  synthetic  apples  " 
first. 

Several  years  ago,  certain  men  and 
in  fact  we  might  say  certain  nations 
began  to  appreciate  the  fact  that  the 
time  was  approaching  when  the 
amount  of  wild  rubber  then  being 
produced  would  not  be  sufficient  to 
supply  the  world's  demands.  To 
meet  this  condition,  Mons.  E.  Coustet 
proposed  three  solutions: 

First,  he  said  we  must  use  the 
mineral  caoutchouc  which  had  been 
discovered  in  the  Castleton  mines, 
England,  in  1785,  and  later  in 
France  in  1816,  and  still  later  in  the 
United  States. 

Second,  we  must  employ  an  arti- 
ficial product  possessing  the  prop- 
erties of  the  natural  product.  In 
1846,  Sacc  and  Jonas  produced  such 
a  substance  by  treating  linseed  oil 
with  azotic  acid.  Another  similar 
substance  had  been  produced  by 
treating  oil  of  turpentine  with  sul- 
phuric acid. 

The  third  suggestion  was  to  in- 
crease the  supply  of  natural  product, 
but  this  seemed  like  a  very  slow 
method. 

The  first  of  these  suggestions  has 
been  utilized  and  in  addition  to  these 
mineral  rubbers  we  are  using  today 
large  quantities  of  synthetic  mineral 
rubber. 

The  third  way  of  course  has 
proved  the  method  which  has  largely 


solved  our  problem  to  date,  for  the 
quantity  of  the  natural  product  has 
been  increased  both  by  obtaining  more 
of  the  wild  rubber  and  by  the  great 
development  of  plantations. 

The  second  idea,  that  of  artificial 
rubber,  however,  still  remains  the 
dream  of  the  chemist.  It  is  not  a 
question  of  merely  producing  it,  for 
that  has  been  accomplished,  but  of 
producing  it  upon  a  commercial 
basis. 

How  great  the  demand  has  been 
for  the  artificial  product  is  reflected 
in  the  following  statement  found  in 
the  Independent  (Sept.  13,  1906, 
61:648-9):  "If  any  ambitious 
young  man  would  like  to  earn  $10,- 
000,000  next  year  he  has  the  chance. 
The  world  will  gladly  pay  him  that, 
or  even  more  if  he  will  showr  how  to 
make  India  rubber  cheaply.  He 
will  find  much  of  the  preliminary 
work  already  done;  only  one  link  is 
lacking  in  the  chemical  process.  All 
he  has  to  do  is  to  reverse  a  well 
known  chemical  reaction.  Any 
freshman  chemist  can  do  it — on 
paper.  This  is  all  there  is  to  it: 

O/^1  TJ  v     C\     TT       » 

4V^5±18  —         — >  Ujo-tlie 

We  know  that  isoprene  results 
from  the  distillation  of  caoutchouc. 
In  1860,  Greville  Williams  isolated 
isoprene  with  the  apparent  formula 
of  C5H8  (Proc.  Roy.  Soc.  I860,  10, 
516)  ;  therefore,  the  above  is  possible 
and  has  been  accomplished,  but  not 
on  a  commercial  basis.  Bouchardat 
in  1875  (Compt.  rend.  1875,  80, 
1446)  had  observed  that  some  of  the 
distillation  products  of  caoutchouc 
could  be  changed  into  rubber  when 
treated  with  hydrochloric  acid  in  the 
cold.  This  substance  was  undoubt- 
edly isoprene.  He  also  called  atten- 


59 


60 


RUBBER    MANUFACTURE 


tion  to  a  polymer  of  this  having  the 
formula  C10H16. 

Isoprene  may  be  made  from  tur- 
pentine. In  1882,  Sir  William  Til- 
den  (Trans.  Chem.  Soc.  1884,  45, 
411)  observed  that  isoprene  could 
be  made  from  terpenes  (substances 
obtained  from  oil  of  turpentine). 
He  also  observed  that  this  isoprene 
upon  long  standing  polymerized  into 
rubber.  Attempts  were  then  made 
to  hasten  this  reaction.  Tilden  made 
his  isoprene  by  passing  oil  of  turpen- 
tine through  pipes  heated  to  a  red 
glow.  If  the  isoprene  may  be 
cheaply  converted  into  caoutchouc, 
then  the  raw  rubber  industry  may  be 
transferred  from  the  rubber  tree  of 
the  tropics  to  the  pine  trees  of  our 
own  country. 

A  British  patent  of  1907,  proposed 
by  Heinemann,  describes  the  process 
of  making  synthetic  rubber  by  heat- 
ing a  mixture  of  acetylene  and  ethy- 
lene  at  a  dull  red  heat  and  there 
results  di  vinyl, 


then  by  the  ordinary  reaction  using 
methylchloride,  this  is  converted  into 
methyl  divinyl,  or  isoprene, 

CH2  =  C  •  CH3  •  CH  "=•  CH2 

Again  the  isoprene  is  made  to  poly- 
merize into  caoutchouc. 

There  was  a  time  when  the  "  syn- 
thetic rubber  scare  "  nearly  pro- 
duced a  panic  in  the  rubber  planta- 
tion securities.  This  furnishes  evi- 
dence of  the  almost  unreasonable 
fluctuation  of  a  stock  market. 

Harries  in  1905  had  established, 
he  thought,  the  chemical  constitution 
of  caoutchouc  to  be  1.5  dimethyl- 
cyclooctadiene  and  this  aided  the 
problem  of  building  up  the  synthetic 
product  (Ear.  1904,  vol.  37,  p.  2708; 
1905,  vol.  38,  p.  1195). 

In  1910,  Harries  reported  in  a 
lecture  given  in  Vienna  that  he  had 
succeeded  in  converting  isoprene 
into  caoutchouc  by  heating  it  in 
sealed  tubes  in  the  presence  of 
glacial  actetic  acid,  and  he  deserves 
the  credit  of  being  the  first  man  to 
publish  a  method  for  this  which 
could  be  repeated  by  another  investi- 
gator. Harries,  in  1911,  found  that 


isoprene  in  the  presence  of  metallic 
sodium  polymerized  very  rapidly, 
but  that  the  product  was  different 
from  the  one  obtained  where  heat  was 
used.  (Annalen,  1911,  vol.  383,  p. 
188). 

In  1884,  Tilden  also  suggested 
that  it  was  possible  to  polymerize 
the  homologues  of  isoprene  and  in  so 
doing  to  obtain  substances  varying 
from  resinous  bodies  up  to  those  pos- 
sessing the  properties  of  rubber. 
This  of  course  suggested  new  mate- 
rials as  starting  products  in  the  pro- 
curing of  synthetic  caoutchouc. 

0.  Wallach  (Annalen,  1884,  225, 
311;  1885,  227,  292;  1887,  238,  88) 
studied  the  behavior  of  isoprene  and 
did  succeed  in  polymerizing  it  by 
means  of  the  action  of  light. 

Weber  repeated  the  work  of  Tilden 
and  reports  that  he  obtained  211 
grams  of  caoutchouc  from  300  grams 
of  isoprene,  after  keeping  it  for  nine 
months. 

In  all  this  work,  it  will  be  observed 
that  the  isoprene  has  been  obtained 
from  some  other  natural  source,  but 
in  1897  Euler  was  able  to  synthesize 
this  substance.  (Ber.  1897,  30,  1989; 
J.  Prakt.  Chem.  1898,  57,  131).  He 
began  with  /3-methyl  pyrrolidine 

/TTT        r'TT      pi 
v^riq "~  v*n  ~"~  \j  J 


CHg — CH^ 

and  by  successive  treatment  with 
CHSI  and  KOH  was  able  to  produce 
isoprene : 

rw  —P  — PTT 

V^-Tlg         O   V^Ilo 

I 

/-ITT    fll 

L>ll   ^Jtlg 

It  is  apparent,  therefore,  that  the 
product  which  results  depends  upon 
the  method  used  and  also  upon  the 
material  used  in  starting,  as  is  shown 
by  the  statements  of  Holt  in  Z.  angew. 
Chem.  1914,  vol.  27,  p.  153. 
Caoutchoucs  from  Butadiene,  C4H6 

Normal  caoutchouc :  (by  heat- 
ing), easily  soluble,  elastic,  vulcan- 
izable. 

Carbon  dioxide  caoutchouc :  In- 
soluble, does  not  swell  up,  moderately 
elastic,  unvulcanizable. 


SYNTHETIC  CAOUTCHOUC 


Sodium  caoutchouc  :     Easily  solu- 
ble, elastic,  vulcanizable. 
Caoutchoucs  from  Isoprene,  C5HS 

Normal  caoutchouc  :  Easily  solu- 
ble, elastic,  vulcanizable. 

Carbon  dioxide  caoutchouc :  In- 
soluble, does  not  swell  up,  elastic, 
vulcanizable. 

Sodium  caoutchouc:  Easily  solu- 
ble, not  elastic,  difficultly  and  incom- 
pletely vulcanizable. 

Caoutchoucs  from  Dimcthylbuta- 
diene,  C«H10 

Normal  caoutchouc :  Easily  solu- 
ble, not  elastic,  can  only  be  vulcan- 
ized to  hard  rubber. 

Carbon  dioxide  caoutchouc :  In- 
soluble, does  not  swell  up,  not  elastic, 
difficultly  vulcanizable,  easily  oxidiz- 
able. 

Sodium  caoutchouc :  Soluble  and 
insoluble  modifications,  not  elastic, 
unvulcanizable. 

From  the  aboye  table,  it  may  be 
seen  that  by  properly  choosing  the 
material  to  start  with,  and  by  use  of 
the  proper  process  of  polymerization, 
it  is  possible  to  obtain  caoutchouc 
with  entirely  different  properties. 


CH 


This  has  a  suggestion  in  it  of  tech- 
nical importance  for  it  points  out  the 
fact  that  some  day  we  may  be  able  to 
produce  and  emphasize  any  particu- 
lar property  that  is  desired. 

The  first  thing  to  be  accomplished 
is  the  production  of  isoprene  or  its 
homologues,  then  a  method  of  polym- 
erizing these  substances.  Both  of 
these  processes  must  be  such  as  can 
be  worked  on  a  commercial  basis  and 
must  produce  a  final  product  with 
chemical  and  physical  properties 
analogous  to  the  native  rubber  and  at 
a  cost  to  compete  with  the  native 
rubber. 

We  shall  now  consider  different 
means  of  producing  isoprene.  It  was 
noted  above  that  Tilden  obtained 
about  a  five  per  cent  yield  of  isoprene 
from  turpentine,  but  even  though  a 
good  yield  could  be  obtained,  the 
supply  of  turpentine  is  very  variable 
and  uncertain.  Several  men  have 
carried  out  valuable  investigations 
along  this  line.  Neresheimer  (Tnaug. 
Dissert.  Kiel,  1911)  began  with  the 
diethyl  ester  of  pyrotartaric  acid, 
which  he  reduced  by  means  of 
sodium  and  then  the  following  steps 
as  indicated  here : 


CHP 


CH 


CH  •  COOC2  H5    Reduction  CH  •  CH2  OH  CH  •  CH2  Br 

I  with  I  with     I 

Sodium  I  HBr    I 

CH2-COOC2H5  CH2   CH2OH  CH2-CH2Br 


CHa 


CH£ 


with       CH  •  CH2  N(CH3)3Br 


N(CH3)3    I  Ag9O' 

3  CH2   CH2N(CH3)3Br    ^2 


CH  •  CH2N(CH3)3  OH 
CH2   CH2N(CH3)3  OH 


CH3 


Distillation, 


C  -H  :  CH2 

This  method  has  the  great  advan- 
tage of  producing  a  pure  product. 
}I  at  thews  and  Strange  (English  Pat. 
4189,  1910)  worked  out  a  different 
method  starting  with  isopentane, 


/-.TT 


CH  •  CH2*  CH3 


first  converting  it  into  the  dihalogen 
compound, 


From  this  the  halogen  acid  is  then 
removed  and  isoprene  results  : 


Then  later  we  find  another  process 
beginning  with  the  same  substance 
when  the  Badischer  Anilin  und  Soda 


62 


RUBBER   MANUFACTURE 


Fabrik  (Fren.  Pat.  43512,  1911)  ob- 
tained isoprene  by  the  following 
steps : 

CH3">CH-CH-CH 
CH3/ 

is   converted   into  the   monohalogen, 

CH; 

CHt 
this  when  treated  with   lime  yields 


trimethylethylene.     This  is  then  con- 
verted into  the  dihalogen  derivative, 


CBr-CHBr   CHq 


and  when  this  is  passed  over  a  cata- 
lytic agent  under  reduced  pressure 
at  a  temperature  of  350  deg.,  isoprene 
results, 


CH 


CH 


C-CH=CHo 


The  Bayer  Co.  next  produced  iso- 
prene, beginning  with  a  coal  tar 
product.  They  used  p-cresol  which 
is  first  reduced  and  then  oxidized 
and  this  treatment  will  break  the 
ring  structure.  The  steps  are  indi- 
cated as  follows: 

CH3 
C 


CH 


A 


CH 


CHl       J 
C 


OH 
CH3 

CH • CH8  COOH 
CHjj'CHjjCOOH 


Reduction  N 
Oxidization' 


CH3 

CH  •  CH2  CONH2    HCIO 

CH2CH2CONH2 

CHa 


CH3 

>CH-CH2NH2 
CH2  CH2  NH3 


Methylation      i,    ~TT       .     . 

— >C:CH2     is  isoprene. 

CH :  CH2 

Heinemann  (Eng.  Pa^.13252, 1908) 
proposed  that  by  the  hydrolysis  of 
starch,  then  oxidization  and  treat- 
ment with  phosphorus  trisulphide, 
there  would  result  methylthiophene 
which  upon  reduction  would  give 
isoprene.  This  is  the  method  which 
gained  wide  newspaper  publicity  for 
it  suggests  the  production  of  auto 
tires  out  of  potatoes. 

Harries  (Annalen,  1911,  383,  157) 
worked  out  a  method  starting  with 
alcohol,  the  necessary  steps  of  which 
method  are  indicated  here : 

CH3  CH2  OH — >CH3  COOH — >CH3  COCH3 

>(CH3)2  •  C(C2H5)OH^CH3-  CH:C:(CH3)S 

~->CH3  CHBr  CBr  (CH3)2 — >CH2:  CH-rt"CH'1 


This  method  becomes  a  possibility 
inasmuch  as  commercial  alcohol  is 
now  available.  It  is  claimed  for  this 
process  that  it  will  yield  from  60  to 
75  per  cent  pure  isoprene. 

Matthews  and  Strange  (Eng.  Pat. 
4572,  1910)  then  carried  out  some 
work  with  the  amyl  alcohols,  both  the 
iso  and  active,  found  in  fusel  oil. 
By  carefully  chlorinating  these  sub- 
stances, passing  the  products  over 
soda  lime  heated  to  470  deg.  and  then 
fractionating,  they  claimed  to  have 
obtained  a  forty  per  cent  yield  of 
isoprene. 

This  constitutes  a  brief  survey  of 
the  attempts  which  have  been  made 
to  produce  isoprene,  the  substance 
which  by  polymerization  we  are  able 
to  convert  into  caoutchouc. 

Next  in  order,  therefore,  we  must 
consider  the  ways  which  we  have  for 
effecting  this  latter  change. 

Some  of  these  have  already  been 
mentioned,  for  example,  its  treat- 


SYNTHETIC  CAOUTCHOUC 


63 


ment  with  acid,  autopolymerization, 
light,  etc.,  all  of  these  processes  being 
slow  and  producing  uncertain  re- 
sults. It  was  to  hasten  this  process 
that  heating  in  sealed  tubes  and  then 
treatment  with  acetic  acid  was  tried. 
From  "the  use  of  these  substances  to 
accelerate  the  change,  we  find  almost 
every  class  of  compounds,  both  or- 
ganic and  inorganic,  being  used,  even 
down  to  the  Roentgen  rays. 

The  caoutchoucs  prepared  by  the 
above  reagents  will  respond  to  tests, 
which  Harries  laid  down  for  a  true 
caoutchouc  and  thus  these  are  called 
"  normal  caoutchoucs." 

Then  Harries  and  Matthews  inde- 
pendently found  that  sodium  or  even 
amalgams,  either  hot  or  cold,  would 
polymerize  isoprene  either  in  the  cold 
or  with  a  little  heat,  and  effect  this 
change  almost  quantitatively.  This 
final  product  does  not  yield  the  same 
ozonide  as  the  normal  caoutchouc,  in- 
dicating that  it  must  possess  a  differ- 
ent constitution.  As  stated  in  the 
beginning,  Tilden  suggested  that  it 
was  possible  to  produce  caoutchouc 
from  the  homologues  of  isoprene; 
also,  therefore,  we  shall  discuss 
briefly  the  one  most  commonly  used 
and  the  one  which  has  given  the  best 
results,  namely,  Butadiene.  Harries 
started  with  ethylmethylketone  and 
reduced  it  to  sec-butyl  alcohol,  which 
may  be  dehydrated,  then  by  produc- 
ing the  dibromide  and  treating  this 
with  soda  lime,  butadiene  results. 

Hexahydrophenol  has  been  con- 
verted into  butadiene  by  heating  it 
to  a  temperature  of  600  deg.  C. 

It  was  observed  by  Ehrlich  in 
1905  that  the  addition  of  amino 
acids  would  increase  the  pro- 
duction of  higher  alcohols  in 


fusel  oil  during  fermentation.  With 
this  idea,,  Fernbach  and  Strange 
worked  out  a  cheap  method  of  pro- 
ducing butyl  alcohol  and  acetone. 
This  alcohol  is  then  converted  into  the 
chloride,  and  then  by  chlorination  into 
the  dichloride,  which  when  heated 
with  soda  lime  will  produce  butadiene, 


VV1LH    Q<J<_tO,   JHU.C     W1JU. 

CH3  CH2  CH2  CH2  OH 
CH3  CH2  CH2  CH2  Cl     — 
CH3  CH2  CHC1  CH2  Cl  or 
CH3CHC1   CH2CH2Clor 
CH2C1   CH2CH2CH2C1 


•CH2=CH-CH=CHa 


The  Synthetic  Products  Co.  suc- 
ceeded in  converting  butyl  aldehyde 
into  the  aldol,  and  this  when  reduced 
gives  the  1,3-butyleneglycol;  this  is 
converted  into  the  dichloride,  and 
when  treated  with  soda  lime  butadi- 
ene results. 


CH3  CHOH  CH2  CHO- 
CH3CHC1CH2CH2C1- 


>CH3  CHOHCHs  CH2  OH- 
>CH2=CH-CH=CH8 
Butadiene 


Several  other  methods  have  been 
used  to  produce  this  substance,  and 
in  fact  several  other  homologues  have 
been  produced.  The  methods  used 
to  polymerize  butadiene  are  similar 
to  the  ones  used  upon  isoprene.  The 
sodium  butadiene  seems  to  be  the 
best,  however.  The  polymerization 
is  complete  in  about  three  hours  if 
it  is  held  at  a  temperature  of  from 
forty  to  fifty  degrees. 

This  constitutes  a  brief  survey  of 
the  synthetic  rubber  industry  up  to 
date.  Although  it  is  very  promising 
from  the  standpoint  of  the  work 
which  has  been  done,  yet  a  great  deal 
more  remains  to  be  done  before  the 
natural  rubber  securities  need  be  dis- 
turbed again  either  in  the  United 
States  or  in  Europe. 


CHAPTER  XI 
Chemical  and  Physical  Testing  of  Crude  Rubber 


As  in  the  analysis  of  every  sub- 
stance, so  in  the  analysis  of  crude 
rubber,  the  chemist  must  first  obtain 
what  may  be  regarded  as  a  uniform 
sample.  This,  at  first  thought,  seems 
a  very  simple  matter,  and  yet  it  is 
one  that  causes  as  much  if  not  more 
trouble  than  any  other  step  in  the 
complete  analysis  of  any  substance. 

It  is  obvious  that  the  analysis  of  a 
few  ounces  of  rubber  is  absolutely 
worthless  unless  the  sample  is  truly 
representative  of  the  entire  «lot  whose 
composition  is  desired.  Therefore,  a 
few  general  directions  are  necessary 
for  the  obtaining  of  what  may  be 
regarded  as  uniform  a  test  lot  as  pos- 
sible. 

Rubber  comes  into  the  market  in 
extremely  varying  forms  and  lots. 
Of  course,  the  more  uniform  the 
rubber  the  easier  it  is  to  obtain  a 
good  sample  and  vice  versa.  The 
plantation  rubber  is  comparative- 
ly easy  to  sample.  It  will  be  re- 
membered that  the  rubber  comes 
into  the  market  in  the  form  of  sheets, 
blocks  or  slabs,  balls,  spindles, 
thimbles,  twists,  sausages,  scraps  of 
every  size  and  shape,  biscuits,  etc. 
Some  shipments  are  small,  others  are 
large ;  some  of  the  above  forms  are 
small  and  some  large.  It  naturally 
follows,  of  course,  that  the  smaller 
the  forms  and  the  smaller  the  ship- 
ments, the  easier  the  task  of  sampling. 

As  an  example,  let  us  select  a  sam- 
ple from  a  large  shipment  made  up 
of  many  containers  of  which  the  forms 
are  rather  large.  Enough  of  the 
containers  should  be  opened  and  thor- 
oughly inspected  to  learn  whether  it 
may  be  regarded  as  a  uniform  ship- 
ment, that  is,  whether  each  package 
is  a  representative  sample  of  the 


whole.  If  this  is  true,  then  a  sample 
need  not  be  taken  from  each  package, 
but  only  from  every  other  one  or 
every  third  one.  This,  of  course,  is 
to  be  judged  from  the  general  appear- 
ance of  the  lot.  If  the  forms  are  also 
running  large,  samples  may  be  cut 
from  representative  ones  taken.  This 
will  keep  the  volume  of  the  sample 
down  and  at  the  same  time  not  impair 
its  uniformity.  When  cutting  a  ball 
or  slab,  it  must  be  cut  completely 
through.  Some  take  a  slice  diagonally 
through  the  form  while  others  take 
one  through  the  middle  perpendicular 
to  the  long  axis.  Ordinarily,  sam- 
pling is  not  pleasant  work  and  is, 
therefore,  sadly  neglected.  A  sample 
is  wanted,  some  inexperienced  help  is 
often  sent  to  get  it  and  he  does  so  with 
the  least  possible  expenditure  of  en- 
ergy and  thought.  Too  much  emphasis 
cannot  be  placed  upon  this  first  and 
very  important  step  in  the  analysis 
of  rubber,  or,  in  fact,  any  substance. 

Washing  Loss 

The  sample  having  been  obtained, 
the  first  thing  to  be  done  is  to  deter- 
mine what  is  called  the  "  washing 
loss."  This  will  include  in  its  per 
cent  that  due  to  moisture,  dirt,  and 
the  soluble  non-rubbers,  which  in- 
clude proteins  and  carbohydrates.  To 
determine  the  washing  loss,  the  larger 
the  sample  taken  the  better;  there- 
fore, this  test  is  better  carried  out  on 
a  factory  scale  than  in  the  laboratory. 
A  batch  of  rubber  is  first  of  all  sub- 
jected to  the  washing  process,  just 
what  method  to  be  used  depending 
upon  the  grade  of  crude  rubber.  If 
it  comes  in  large,  somewhat  hard 
forms,  it  may  be  softened  first  in 
warm  water  and  then  cut  up  into 
suitable  sizes  to  pass  through  the 


64 


CHEMICAL  AND  PHYSICAL  TESTING  OF  CRUDE  RUBBER 


65 


washer.  The  rolls  are  set  rather  far 
apart  at  first  and  water  plays  over 
them.  As  the  rubber  passes  between 
the  rolls,  it  soon  takes  the  crepe  form 
and  the  washing  continues  until  the 
impurities  are  all  removed.  The  rolls 
are  gradually  brought  closer  together 
so  that  a  thin  crepe  may  be  obtained, 
thus  enabling  the  rubber  to  dry  more 
quickly.  The  thickness  of  these  sheets 
varies  greatly  in  different  factories. 
After  this  it  is  dried  and  the  loss  in 
weight  which  it  suffers,  calculated  in 
per  cent  of  the  original  batch,  repre- 
sents the  "  washing  loss." 

This  is  a  test  which  has  great  in- 
fluence in  determining  the  value  of 
wild  rubbers.  On  account  of  the 
cleanly  methods  of  handling,  the 
plantation  rubbers  run  the  lowest  in 
washing  loss  while  some  grades  of 
African  run  over  fifty  per  cent  wash- 
ing loss. 

A  list  of  the  more  common  rubbers 
with  their  average  results  of  analysis 
is  given  on  another  page.  If  the  de- 
termination has  to  be  carried  out  on  a 
laboratory  basis,  great  care  must  be 
exercised  in  selecting  the  sample,  for 
misleading  results  may  be  obtained 
unless  it  is  very  carefully  supervised. 

From  the  analysis  of  crude  rubber, 
not  a  great  deal  is  to  be  gained.  We 
shall  present  the  tests  ordinarily  car- 
ried out  in  the  order  of  their  im- 
portance. 

Determination  of  Moisture 

First,  the  moisture  present  in  rub- 
ber must  be  determined.  Moisture  may 
cause  a  great  deal  of  trouble  in  differ- 
ent manufacturing  processes  and, 
therefore,  before  being  used,  the  rub- 
ber must  be  thoroughly  dried.  This  is 
a  test  which  it  is  not  necessary  to  carry 
out  in  the  chemical  laboratory  very 
often,  for  a  man  with  much  ex- 
perience in  handling  rubber  is  soon 
able  to  judge  as  to  the  amount  of 
moisture  present  in  a  sample,  or  at 
least  as  to  whether  or  not  it  is  dry 
enough  to  be  used  in  compounding. 
If  it  is  imperative  to  carry  out  this 
test  in  order  to  trace  some  trouble, 
then  the  best  method  consists  in  heat- 
ing five  to  ten  grams  of  the  sample, 
reduced  to  as  small  parts  as  possible. 


in  a  vacuum  oven  until  it  comes  down 
to  a  constant  weight.  This  will  re- 
quire only  a  short  time  with  some  rub- 
bers and  a  comparatively  long  time 
with  others.  Sometimes  wre  see  this 
test  being  carried  out  in  an  ordinary 
hot-air  oven.  Comparative  results 
may  be  obtained  by  this  method,  but 
it  is  not  to  be  recommended.  The 
best  and  most  accurate  method  con- 
sists in  allowing  the  rubber  to  stand 
over  sulphuric  acid  in  a  vacuum  dis- 
sicator  at  normal  temperature. 

The  tendency  of  rubber  to  oxidize 
with  elevation  of  temperature  must  be 
guarded  against.  The  unvulcanized 
rubber  is  less  susceptible  to  this  in- 
fluence than  the  vulvanized. 

Theoretically,  wre  want  to  dry  the 
rubber  in  the  shortest  possible  time 
at  the  lowest  temperature  possible. 
This,  of  course,  is  effected  by  drying 
in  a  vacuum,  the  temperature  used 
being  generally  about  60  deg.  C.  If 
a  hot-air  oven  must  be  used,  105-110 
deg.  C.  is  used.  At  this  temperature 
and,  in  fact,  at  60  deg.  C.,  some  rub- 
bers running  high  in  a  flabby  resin 
become  very  soft  and  tacky  and  it  is 
hard  to  remove  the  last  traces  of  mois- 
ture, likewise  they  are  more  apt 
to  oxidize.  To  obviate  the  difficulty 
of  oxidization,  during  the  drying. 
Obach  devised  a  method  whereby  he 
dried  the  rubber  in  a  stream  of  dry 
carbon  dioxide  and  then  absorbed  the 
moisture  in  a  weighed  U-tube  contain- 
ing sulphuric  acid.  This  method  de- 
termines the  moisture  directly,  but  is 
more  or  less  difficult  to  control. 

The  percentage  of  moisture  by  what- 
ever method  determined,  is  calculated 
from  the  ratio  of  the  loss  during  heat- 
ing to  the  amount  taken  in  the  be- 
ginning. As  a  limit  of  water  present 
in  rubber  for  compounding,  we  may 
allow  as  high  as  0.5  of  a  per  cent.  As 
before  stated  it  is  necessary  only  to 
perform  this  test  occasionally  to  check 
up  the  efficiency  of  the  drying  system 


in  use. 


Estimation  of  Resin 


The  next  determination  is  the  one, 
which  is  no  doubt  carried  out  more 
than  any  other,  namely,  the  estima- 
tion of  the  amount  of  resin.  The  prin- 
ciple, upon  which  this  determination 


66 


RUBBER   MANUFACTURE 


is  based,  consists  in  extracting  a 
known  weight  of  the  washed  and 
dried  rubber  with  a  solvent  which 
will  remove  the  resin.  Acetone  is  the 
one  used.  The  solvent  is  then  evapo- 
rated in  a  weighed  flask  and  the  resin 
thus  determined. 

To  actually  carry  out  this  test  you 
should  proceed  as  follows :  A  weighed 
amount  of  rubber,  which  has  been 
washed  and  dried,  is  placed  in  an  ex- 
tractor, and  here  we  might  say  that 
the  form  used  depends  on  the  wish 
of  the  operator.  Many  different 
forms  are  on  the  market.  Of  course, 
the  Soxhlet  form  is  good  and  has 
been  and  still  is  used  a  great  deal. 
The  Wiley  extractor  has  been  used 
with  considerable  success.  The  writer, 
however,  at  present  is  using  the 
Bailey- Walker  form  and  is  well  sat- 
isfied with  its  results.  The  great  ad- 
vantage in  it  comes  in  its  compact- 
ness and  the  fact  that  the  solution  of 
the  resin  in  acetone  does  not  have  to 
be  transferred  to  a  tared  flask  for 
weighing.  The  acetone  used  in  these 
determinations  should  be  freshly  dis- 
tilled off  from  potassium  carbonate. 

The  larger  the  amount  of  rubber 
taken,  the  more  accurate  will  be  the 
result;  therefore,  let  the  size  of  the 
thimble  in  the  extractor  determine 
how  much  it  is  possible  to  take.  The 
rubber  is  reduced  to  as  small  pieces  as 
possible  so  that  the  maximum  solvent 
action  of  the  acetone  will  be  had. 
Some  rubbers  when  treated  in  this 
manner  and  then  subjected  to  extrac- 
tion, become  very  soft  and  tend  to 
flow  together,  thus  making  complete 
extraction  impossible.  In  cases  of 
this  kind,  the  rubber  may  be  sheeted 
out  as  thin  as  possible  on  a  mill.  Then 
a  Aveighed  ribbon  of  this  is  rolled  up 
in  muslin  and  placed  in  the  extrac- 
tion thimble.  The  extraction  is  then 
begun  by  heating  the  acetone  in  the 
flask  either  over  a  Avater  bath  or  elec- 
tric hot  plate  and  continued  for  a 
period  of  ten  hours.  This  is  ample 
time  for  the  extraction  if  the  sample 
has  been  properly  prepared  and  the 
necessary  precautions  taken.  The  ace- 
tone is  then  evaporated  off  over  a 
water  bath  and  the  flask  is  heated 
for  three  hours  in  an  oven  held  at 
105  to  100  deg.  C 


One  must  be  very  careful  as 
some  resins  are  volatile  at  this  tem- 
perature and  thus  a  loss  might  be  en- 
countered. In  fact,  it  was  recently 
observed  in  our  laboratory  that  there 
were  present  in  some  rubbers  resin 
which  would  volatilize  at  just  a  few 
degrees  above  the  boiling  point  of 
acetone.  It  is  still  an  undecided  ques- 
tion in  the  mind  of  the  writer  as  to 
whether  or  not  there  are  some  which 
distill  over  with  the  acetone. 

The  percentage  of  resin  is  calculated 
on  the  basis  of  the  rubber  taken.  The 
resin  content  varies  within  wide 
limits  when  we  are  considering  all 
kinds  of  rubber,  but  varies  within 
narrow  limits  for  the  same  variety  of 
rubber.  For  instance,  Hevea  will 
run  about  3 — 4  per  cent;  plantation 
about  2 — 3  per  cent,  while  Accra 
Lump  will  run  from  30 — 40  per  cent. 
The  resins  from  South  American  rub- 
bers are  generally  liquid  and  of  a 
dark  color.  Plantation  resins  are  also 
liquid,  but  of  a  lighter  color.  The 
African  resins  are  generally  yellow 
and  more  or  less  brittle,  but  soften 
with  heat. 

The  amount  of  resin  in  a  rubber  is 
not  an  absolutely  reliable  criterion 
as  to  the  value  of  rubber  for  manu- 
facturing purposes.  Ordinarily  the 
low  resin  content  rubbers  are  best  for 
the  resin  may  be  considered  really  as 
a  diluent. 

Determination  of  Ash 

The  next  determination  of  value  is 
that  of  ash.  The  principle  of  this 
determination  consists  simply  in  in- 
cinerating a  weighed  amount  of 
washed  and  dried  rubber  and  thus 
obtaining  the  amount  of  mineral  mat- 
ter in  the  sample. 

To  carry  out  this  test,  as  large  a 
sample  as  possible  is  used  and  weighed 
into  a  large  shallow  formed  crucible 
of  known  weight.  Heat  is  very  care- 
fully applied  and  regulated  so  that 
the  volatile  substances  will  not  take 
fire.  Should  this  happen,-  they  may 
be  easily  extinguished  by  superim- 
posing the  cover  over  the  crucible. 
When  the  volatile  products  are  re- 
moved, the  heat  is  increased  up  to 
that  of  dull  redness  and  held  there 


CHEMICAL  AND  PHYSICAL  TESTING  OF  CRUDE  RUBBER 


67 


until  all  carbonaceous  material  has 
disappeared.  The  weight  of  the  re- 
sidue is  then  obtained  and  its  per- 
centage calculated  on  the  basis  of  the 
rubber  taken. 

The  ash  content  of  rubbers  does  not, 
or  rather  should  not,  vary  within  large 
limits.  In  fact,  in  the  majority  of 
rubbers,  regardless  of  their  source,  the 
per  cent  should  run  from  about  0.5 
of  one  per  cent  up  to  1.5  per  cent. 
There  are  a  few  exceptions  to  this, 
however,  and  we  find  an  ash  as  high 
as  3  per  cent.  The  determination  of 
the  ash  is  of  value  for  two  reasons: 
First,  it  serves  as  a  check  upon  the 
effectiveness  of  the  washing  process, 
for  if  it  has  been  done  hastily  and  in- 
completely, the  ash  will  of  necessity 
run  high.  Secondly,  it  serves  as  a 
means  of  detecting  non-rubber  mate- 
rials. These  determinations  are  the 
chemical  tests  most  frequently  carried 
out  and  the  ones  upon  which  the  ver- 
dict of  the  investigator  is  largely 
based. 

Determination  of  Nitrogen 

Where  a  complete  analysis  is  re- 
quired, it  becomes  necessary  to  de- 
termine the  proteids  and  other  nitro- 
genous matter  in  the  rubber.  These 
cannot  be  determined  directly,  but  we 
simply  multiply  the  amount  of  nitro- 
gen found  by  analysis  by  the  factor 
6.25.  Not  knowing  the  true  nature  of 
the  rubber  proteins,  it  is  hardly  neces- 
sary to  say  that  this  test  does  not  fur- 
nish us  with  any  reliable  information. 
The  test  is  carried  out  as  follows: 
About  two  grams  of  rubber  are 
weighed  out  and  placed  in  a  long- 
necked  Kjeldahl  flask,  when  30  cc.  of 
concentrated  sulphuric  acid  and  a 
drop  of  mercury  are  added.  It  is  well 
to  loosely  cork  the  flask  by  putting  a 
small  funnel  in  the  neck  of  the  Kjel- 
dahl. Heat  is  then  applied  to  the  flask, 
very  carefully  at  first,  until  the  first 
violent  reaction  has  subsided.  Then 
the  heat  is  gradually  increased  until 
the  acid  boils  quite  vigorously.  This 
is  continued  until  the  contents  of  the 
flask  acquire  a  straw  yellow  color. 

The  solution  is  very  cautiously 
diluted,  and  in  some  cases  trans- 
ferred into  a  larger  flask,  although  the 
iising  of  a  large  Kjeldahl  in  the  be- 


ginning avoids  this  step.  After  dilu- 
tion, one  or  two  grams  of  sodium  sul- 
phide are  added,  then  caustic  soda, 
until  the  solution  is  distinctly  alka- 
line. A  few  pieces  of  scrap  zinc  will 
prevent  pounding  when  it  comes  to 
distillation. 

The  nitrogen  of  the  original  rubber 
lias  been  converted  into  ammonium 
sulphate  by  the  above  treatment. 
Upon  the  solution  having  been  made 
alkaline  and  upon  the  application  of 
heat,  ammonia  will  be  distilled  over 
into  a  known  amount  of  N/5  sul- 
phuric acid.  When  the  ammonia  is 
all  driven  over,  the  excess  of  acid  is 
titrated  back  with  N/5  alkali,  using 
methyl  orange  as  an  indicator.  From 
the  amount  of  acid  consumed  during 
the  distillation,  the  amount  of  nitro- 
gen in  the  rubber  taken  is  calculated 
and  from  this  the  protein.  The  nitro- 
gen in  some  unwashed  rubbers  may 
run  as  high  as  one  per  cent.  Of  this 
considerable  •  is  due  to  albuminoids 
which  are  present  in  the  rubber,  but 
which  are  soluble  and  would  be  re- 
moved upon  washing.  It  is  the  al- 
buminoid nitrogen  which  undergoes 
putrefaction  and  imparts  to  the  rub- 
ber a  bad  odor.  It  also  has  a  dele- 
terious effect  on  the  rubber.  This 
albuminoid  nitrogen  is  sometimes 
determined  by  determining  the  dif- 
ference between  the  nitrogen  in  the 
unwashed  and  washed  rubber.  A 
small  percent  of  nitrogen  in  rubber 
is  a  sign  of  strength  rather  than  of 
weakness  in  the  rubber. 

Determination  of  Insoluble  Matter 

The  determination  of  insoluble 
matter  is  sometimes  required.  As  the 
term  implies,  it  includes  those  sub- 
stances which  are  insoluble  in  the 
ordinary  rubber  solvents.  Under  in- 
soluble matter,  we  find  sand,  clay, 
wood,  humus,  and  other  accidental 
impurities. 

Theoretically  it  is  an  easy  matter 
to  treat  a  known  amount  of  rubber 
with  a  solvent  and  weigh  the  residue, 
thus  obtaining  the  insoluble  matter, 
but  the  extreme  viscosity  of  rub- 
ber solutions  makes  it  a  difficult  mat- 
ter to  separate  the  insoluble  from 
the  soluble. 


68 


RUBBER    MANUFACTURE 


The  methods  employed  give  best 
results  if  the  crude  rubber  is  first 
milled  when  the  pectus  modification 
is  broken  down,  and  solution  results 
more  readily.  A  known  amount  of 
rubber  is  treated  with  either  toluene 
or  phenetol,  the  latter  having  been 
used  by  C.  Beadle  and  H.  P.  Stevens. 
Even  petroleum  may  be  used  and 
gives  a  solution,  which  may  be  fil- 
tered through  a  tared  filter  or  centi- 
fuged  and  the  residue  determined. 

Determination   of  Rubber 

The  insoluble  matter  as  a  rule  runs 
a  little  lower  than  the  ash  as  some 
of  the  inorganic  matter  exists  as  salts 
which  are  soluble  in  the  solvents 
used.  The  determination  of  rubber 
proper,  or  the  pure  hydrocarbon,  is 
generally  obtained  by  difference,  that 
is,  the  combined  percentage  of  mois- 
ture, ash,  organic  protein,  and  ace- 
tone extract  subtracted  from  100.  It 
may  be  determined  directly,  how- 
ever. One  or  two  grams  of  rubber 
are  put  into  solution  as  indicated 
under  insoluble  matter  and  then  al- 
lowed to  settle  of  its  own  accord,  or 
is  hastened  by  centrifugal  force.  It 
is  diluted  up  to  100  cc.  and  then 
50  cc.  are  pipetted  off  and  dropped 
into  100  cc.  of  warm  alcohol,  when 
the  pure  hydrocarbon  is  precipitated. 
To  purify  it  the  caoutchouc  is  pre- 
cipitated several  times,  then  dried  in 
a  weighed  disk  in  a  vacuum  and  its 
weight  determined. 

Instead  of  precipitating  the  rub- 
ber from  the  50  cc.  of  solution  it 
might  have  been  transferred  to  a 
weighed  flask,  and  the  solvent  evapo- 
rated off.  The  resin  can  then  be  re- 
moved by  repeated  washing  with 
boiling  alcohol  under  a  reflux  con- 
denser. It  may  then  be  dried  and 
its  weight  ascertained.  The  higher 
the  resin  content,  the  less  accurate 
are  both  of  these  methods. 

Its  determination  by  formation  of 
the  tetrabromide  has  been  outlined 
by  Spence  and  Galletly.  They  first 
dissolved  a  small  amount  of  rub- 
ber in  carbon  tetrachloride.  To  this 
they  added  a  reagent  composed  of 
6  cc.  of  bromine  and  one  gram  of 
iixline  in  one  liter  of  carbon  tetra- 
chloride, and  allowed  to  remain  about 


six  hours.  When  this  solution  is 
added  to  alcohol,  the  tetrabromide  is 
precipitated.  It  may  be  purified  by 
dissolving  it  in  carbon  disulphide 
and  reprecipitating  it  with  petroleum 
ether.  This  may  be  repeated  if  nec- 
essary. The  pure  tetrabromide  is 
then  fused  with  a  mixture  of  sodium 
carbonate  and  potassium  nitrate.  The 
residue  is  taken  up  in  a  small  amount 
of  water,  nitric  acid  added,  boiled 
and  the  silver  halide  determined. 
From  this  the  amount  of  rubber 
proper  is  calculated.  A  great  deal 
has  been  published  concerning  this 
method  and  it  has  its  merits  in  prin- 
ciple at  least,  but  in  the  hands  of  the 
writer,  it  has  never  given  concordant 
results. 

Viscosity  of  Rubber 

Schidrowitz  and  Goldsbrough 
(J.S.C.L,  1909,  p.  3)  have  called  at- 
tention to  some  very  interesting  re- 
sults from  experiments  upon  the  vis- 
cosity of  rubber  and  its  solutions. 
They  point  out  that  as  is  known,  the 
viscosity  of  a  liquid  or  of  a  solid 
contained  in  a  liquid  depends  upon 
the  state  of  aggregation  of  the  mole- 
cules or  physical  aggregation.  There- 
fore, the  viscosity  of  rubber  solu- 
tions should  throw  some  light  upon 
the  chemical  or  physical  state  of  ag- 
gregation in  the  rubber  solution  and 
this  should  give  some  idea  as  to  the 
"  nerve  "  of  the  rubber  under  con- 
sideration. The  results  of  this  work 
lead  Schidrowitz  to  conclude  that 
"  Within  the  same  species,  viscosity 
measurements  give  a  direct  line  as 
to  strength  and  vulcanizing  capac- 
ity. Comparing  species  with  species, 
this  does  not  hold  good  directly, 
probably  because  different  species 
possess  differently  constituted  mole- 
cules, and  the  relationship  is,  there- 
fore, of  a  more  complex  order  than  be- 
tween different  specimens  of  the  same 
species.  At  the  same  time  the  broad 
proposition  holds  good  for  all  species, 
compared  inter  se  or  otherwise,  that 
high  viscosity  figures  indicate 
strength  and  low  viscosity  figures, 
weakness. ' ' 

Specific  Gravity 
Specific   gravity   is   sometimes   de- 


CHEMICAL  AND  PHYSICAL  TESTING  OF  CRUDE  RUBBER 


69 


termined,  any  one  of  the  general 
methods  for  such  work  being  em- 
ployed. The  information  to  be  gained 
from  this  determination  does  not  in- 
fluence the  judgment  of  the  investi- 
gator to  any  extent.  Only  on  rare 
occasions  is  it  carried  out  on  crude 
rubber,  but  it  is  used  a  great  deal  on 
vulcanized  goods. 

Sun  Cracking 

Another  test,  which  has  been  sug- 
gested to  be  used  upon  both  crude 
and  vulcanized  rubber,  is  known  as 
the  effect  of  "  sun  cracking." 

To  test  the  liability  of  rubber  to 
sun  crack  requires  a  long  period  of 
time,  and  that,  of  course,  renders  the 
test  almost  useless  because  we  do  not 
have  time  to  waste  in  waiting  for  a 
test  that  consumes  a  large  amount  of 
time.  However,  to  obtain  a  test, 
which  will  show  this  property  of  the 
rubber,  several  artificial  methods 
have  been  recommended.  Weber  sub- 
jected weighed  samples  of  rubber, 
presenting  the  same  area,  to  the  ac- 
tion of  acetone  peroxide  for  two  days. 
The  samples  were  then  removed, 
dried,  weighed,  and  the  increase  in 
weight  was  to  be  considered  as  a 
measure  of  the  liability  of  the  rubber 
to  sun  crack.  He  claims  that  the  re- 
sults obtained  were  in  agreement 
with  the  actual  results  obtained  by 
carrying  out  the  sun-cracking  test. 

Ditmar  tried  to  obtain  a  set  of 
comparative  results  illustrating  the 
same  property  of  rubber.  He  placed 
in  glass  tubes  weighed  samples  of 
rubber,  then  passed  oxygen  into  these 
until  the  air  was  all  excluded,  when 
the  tubes  were  sealed.  These  were 
then  heated  in  a  Carius  furnace  for 
from  five  to  twenty  hours  at  a  tem- 
perature of  100  deg.  C.  The  sam- 
ples of  rubber  were  then  removed 
and  weighed  and  their  increase  in 
weight  he  hoped  to  be  a  measure  of 
the  liability  of  the  rubber  to  sun 
crack.  He  later  modified  his  test  by 
placing  the  rubber  in  a  tube  supplied 
with  ground  valves  at  each  end  and 
he  maintained  a  constant  tempera- 
ture by  lowering  this  tube  into  boil- 
ing water.  Whether  the  results  ob- 


tained are  of  much  value  is  a  ques- 
tion. 

Vulcanizing  Test 

After  all  of  these  tests  have  been 
outlined  and  after  a  sample  has  been 
subjected  to  all  of  them,  the  question 
which  would  still  remain  unanswered 
is  the  one,  which  is  perhaps  oftenest 
asked  by  the  manufacturer:  How 
will  the  rubber  conduct  itself  dur- 
ing vulcanization?  It  is  true  some 
general  idea  of  this  may  be  inter- 
preted from  the  results  obtained 
above,  but  the  only  conclusive  infor- 
mation is  to  be  gained  by  trying  it. 

In  fact,  some  laboratories  base 
their  entire  opinion  of  crude  rubber 
upon  the  information  gained  by  ac- 
tual vulcanizing  and  physical  tests 
which  follow. 

A  certain  test  formula  is  agreed 
upon  and  all  samples  of  rubber  to  be 
tested  are  milled  up  according  to  this 
and  then  subjected  to  vulcanization 
at  a  certain  temperature.  Samples 
are  removed  at  equal  intervals  and 
thus  the  rate  of  cure  in  the  rubber 
may  be  obtained.  Tensile  strength 
strips  may  then  be  made  and  the 
physical  tests  carried  out.  These  are 
the  tests  which  interest  the  practical 
man.  Little  does  he  care  whether  a 
sample  of  rubber  runs  high  or  low  in 
resins  if  it  will  cure  in  a  short  time 
and  produce  what  he  regards  as  a 
good  stock.  The  technical  man,  on 
the  other  hand,  is  interested  in  try- 
ing to  figure  out  the  relation  and  in- 
fluence of  each  of  the  above  tests 
upon  the  product  finally  to  be  ob- 
tained in  actual  working  conditions. 

In  addition  to  all  the  foregoing  in- 
formation, before  final  judgment  is 
pronounced  in  regard  to  a  given  sam- 
ple of  rubber,  its  life  history  should 
be  known:  where  it  came  from,  how 
it  was  obtained,  to  what  species  it 
belongs,  how  it  was  coagulated,  how 
it  was  stored,  its  form,  color,  odor, 
and  many  more  questions  of  a  simi- 
lar nature. 

With  all  of  this  knowledge  before 
one,  a  proper  conclusion  in  regard  to 
the  merits  of  a  sample  of  rubber 
should  be  easily  arrived  at. 


70 


RUBBER   MANUFACTURE 


Below  is  a  table  taken  from  Cas- 
pari,  which  shows  the  relations  of 
different  rubbers  in  regard  to  the 
three  most  important  tests: 

Washing 

Rubber.                Loss.      Resin.  Ash. 
Para    Hard     Fine, 

Para,    Bolivian   Fine..  16-21     2.5-3.5  0.2-0.4 

Manaos    Scrappy 20-25     1.6-2.0  0.6-0.7 

Para      Negrohead,      Ser- 

nambv     30-40     3.0-6.0  0.5-1.5 

Cameta' 45-50     1.4-1.8  0.5-0.8 

Mattogrosso    Virgin 18-22     2.5-3.0  0.5-0.7 

Mattogrosso    Negrohead. .  20-25     1.5-2.0  1.5-2.0 

Mollendo  Fine 15-20     1.8-2.0  0.2-0.3 

Mollcndo    Coarse 12-18     2.0-2.5  0.3-0.4 

Caucho  &  Peruvian  Ball.20-30     3.0-5.0  0.5-1.5 

Manicoba    25-35     2.8-3.0  3.0-4.5 

Ceara    Negrohead 20-30     4.0-5.0  1.0-1.5 

Mangabeira    30-40      20-25  1.0-1.5 

Central   American 20-40     4.0-7.0  1.0-2.5 

Guayule    22-26      20-35  1.0-1.5 


Sierra     Leone,     Conakry, 

Massai,    Soudan 15-30 

Bassam,  Cape  Coast,  Ac- 
cra, Labou.  Ivory  Coast, 

Gold    Coast 25-40 

Second-Accra  Lump,  Salt- 
pond 30-40 

Gambia,    Bissao 30-50 

Gaboon,     Loango,     Congo 

Ball 25-35 

Lagos,    Niger,    Penin 30-40 

Batanga,  Cameroon 25-35 

Lower  Congo.  Wamba . .  .  10-20 
Angola,  Loanda,  Benguela. 25-40 

Upper  Congo  sorts 5-15 

Mozambique,    Beira 7-15 

Madagascar,      Tamatave. 

Majunga  20-30 

Assam     15-35 

Penang    15-30 

Borneo    35-45 

Java  Plantation 1-2 

Ceylon  and  Malayan  Plan- 
tation         1-2 

Plantation    Rambong.  .  .  .    1-2 


5.0-7.0 

0.4-1.0 

7.0-11 

0.7-1.0 

29-38 
5.0-6.0 

1.4-2.0 
1.0-2.0 

8.0-18 
10-25 
10-15 
5-6 
5-7 
4-10 
5-8 

0.6-1.0 
0.3-0.7 
0.5-1.0 
0.5-1.0 
1.0-2.0 
0.5-1.5 
0.1-0.8 

7-10 
5-11 
5-7 
10-11 
5-6 

0.2-0.5 
0.5-1.0 
0.3-0.7 
0.4-0.6 
0.3-0.4 

2.5-3.5 

7-8 

0.2-0.6 
0.2-0.3 

CHAPTER  XII 
The  Manufacture  and  Use  of  Inorganic  Fillers 


It  will  be  our  idea  in  this  chap- 
ter to  give  the  reader  some  infor- 
mation in  regard  to  the  manu- 
facture of  the  materials  which  are 
used  in  compounding  rubber  and 
why  certain  materials  are  used.  In 
the  vast  majority  of  cases,  little  is 
known  of  the  substances  used  in  com- 
pounding and  it  seems  that  the  in- 
creasing of  this  knowledge  should  add 
interest  to  the  subject  and  everyone 
will  grant  that  increased  interest 
tends  toward  greater  efficiency. 

Far  be  it  from  us  to  deal  at  any 
length  with  all  the  inorganic  com- 
pounding ingredients,  or  even  to  men- 
tion them.  We  shall  simply  pick  out 
what  may  be  regarded  as  the  com- 
monest ones,  those  used  in  practically 
every  factory  to  a  greater  or  less 
extent. 

In  order  to  present  this  matter  in 
some  definite  system,  the  writer  will 
group  these  ingredients  under  four 
headings : 

First — Substances  essential  for  vul- 
canization. 

Second — Accelerators. 

Third— Fillers. 

Fourth — Pigments,  which  will  be 
subdivided  into  classes  according  to 
colors. 

This  is  not  the  only  classification 
and  perhaps  it  is  not  the  best  one  but 
it  will  serve  our  purpose  here.  These 
different  groups  overlap  as  will  be 
seen  from  the  order  which  follows. 

Under. the  first  group  we  shall  con- 
sider sulphur,  which  we  may  say  is 
essential  in  all  processes  of  vulcani- 
zation; sulphur  chloride;  carbon  bi- 
sulphide and  carbon  tetrachloride. 
which  are  used  in  certain  kinds  of 
vulcanization. 

Under  the  second  class,  inorganic 
accelerators,  the  few  we  shall  con- 


sider are  the  ones  commonly  used, 
namely : 

Litharge.  Lime, 

White  lead,  Magnesia  calcined, 

Sublimated  white  Magnesia  c  a  r  b  o- 

lead,  uate, 

Red  lead,  Magnesite. 

Under  the  -third  class,  fillers,  we 
shall  discuss  substances  which,  as  the 
name  implies,  may  be  obtained  on 
the  market  at  a  price  to  enable  the 
manufacturer  to  use  them  in  large 
quantities,  substances  which  chem- 
ically are  more  or  less  inert,  such  as 
Barytes,  Kaolin,  China  Clay. 

Alumina  oxide,  Talc,  Soapstone, 

Aluminum  Flake,        Fossil  Flour, 
Whiting,  Asbestos, 

Clays,  Blue  Lead, 

Silica  (Atmoid),         Magnesite. 

There  are  several  more  which 
might  be  classified  here  but  seem  bet- 
ter to  appear  in  the  fourth  group, 

pigments : 

White  Pigments 

Zinc  white,  Barium  sulphate. 

Lithopone.  Barytes, 

Zinc  sulphide.  Kaolin. 

Red  or  Brown  Pigments 
Antimony  Crimson.     Vermilion. 
Antimony  Golden,       Venetian  Red, 
Rouge.  Indian  Red. 

Red  Ochre, 

Black   Pigments 
Lamp  Black,  Graphite. 

Bone  Black,  Lead  sulphide. 

Hydrocarbon, 

Yellorc  Pigments 

Yellow  Ochre.  Cadmium  sulphide. 

Chrome  Yellow,          Arsenic  sulphide. 

Green  Pigments 

Chrome  Green.  Rinmann's  Green. 

Ultramarine  Green. 

Blue  Pigments 

Ultramarine  Blue.      Prussian  Blue, 
Thenard's  Blue,          Chrome  Blue. 

Above  are  the  substances  which 
will  be  dealt  with  in  this  chapter. 

Sulphur 

The  substance,  sulphur,  with  which 
every  man  in  a  rubber  factory  is  ae- 


71 


72 


RUBBER   MANUFACTURE 


quainted,  was  also  known  to  the 
ancients,  for  Homer  900  B.C.  re- 
corded that  it  was  used  in  medicine 
and  in  fumigation.  In  800,  Gebir 
put  forth  the  idea  that  all  metals 
were  compounds  of  sulphur  and  mer- 
cury and  that  it  was  possible  to 
change  from  one  metal  to  another  by 
changing  the  ratio  between  these  two 
substances.  Lavoisier  was  the  first 
to  recognize  it  as  an  element. 

The  use  of  sulphur  in  rubber,  how- 
ever, remained  a  secret  until  Good- 
year, in  1839,  and  Hancock  indepen- 
dently in  1844,  showed  its  effect  upon 
rubber  when  heated  in  contact  with 
it. 

This  element  occurs  in  many  dif- 
ferent ways  in  nature  and  is  well  dis- 
tributed over  the  earth.  It  is  found 
in  the  free  state  in  large  quantities 
in  Sicily  and  Louisiana.  It  occurs 
in  the  form  of  sulphides  of  the  metals 
like  iron,  copper,  lead  and  zinc;  in 
the  form  of  hydrogen  sulphide  in  cer- 
tain springs;  as  sulphur  dioxide  is- 
suing from  volcanoes;  as  sulphates 
of  many  elements  like  lead,  barium, 
calcium,  and  strontium;  then  in  or- 
ganic substances  like  albumen,  horn, 
etc.  We  must  realize,  therefore,  the 
great  distribution  of  this  element  in 
nature. 

It  has  been  estimated  that  the  de- 
posits of  sulphur  in  Sicily,  still  un- 
touched, contain  fifty-five  million 
tons,  and  that  it  will  require  about 
one  hundred  years  to  exhaust  them. 
Up  to  the  year  1900,  it  is  claimed 
that  95  per  cent  of  the  world's  pro- 
duction of  sulphur  came  from  Sicily, 
but  in  1908,  the  United  States  pro- 
duced 45  per  cent  of  that  amount, 
and  from  that  date  has  continued  to 
produce  more  and  more. 

Just  a  few  words  in  regard  to  the 
methods  used  in  Sicily  and  the 
United  States  for  obtaining  sul- 
phur. In  Sicily,  the  sulphur  is  found 
from  150  to  600  feet  below  the  sur- 
face of  the  earth.  It  is  reached  by 
inclined  winding  shafts.  In  earlier 
times,  all  of  the  sulphur  was  brought 
to  the  surface  upon  the  backs  of  men, 
women,  and  children,  but  modern 
methods  of  mining  are  in  general  use 
there  now,  and  it  is  raised  by  me- 
chanical means. 


The  ore  is  first  graded  into  rich, 
good  and  ordinary  lots.  These  ores 
were  formerly  made  into  piles  and 
then  fire  was  set  to  the  piles.  As 
part  of  the  sulphur  burned,  its  heat 
of  combustion  would  melt  the  re- 
mainder, which  would  run  down 
through  the  pile  and  collect  in  a 
trench  around  the  original  heap.  This 
method,  of  course,  caused  a  great 
loss,  and  in  addition,  the  vapors  of 
sulphur  dioxide  damaged  the  health 
of  the  people  and  killed  the  vegeta- 
tion for  miles  around.  By  this  method 
only  about  25  per  cent  of  the  sul- 
phur was  actually  obtained. 

Next  in  line  of  advancement  came 
the  method  of  building  larger  heaps 
of  ore  and  covering  them  over  with 
earth,  just  leaving  here  and  there 
shafts  through  the  heap.  Wood  was 
placed  in  these  shafts  and  kindled. 
Some  of  the  sulphur  would  burn  and 
thus  melt  the  remainder,  which  was 
collected.  These  piles  would  re- 
quire from  one  to  two  months  to 
burn  out.  From  these  as  high  as  60 
per  cent  of  sulphur  was  obtained. 

The  next  improvement  came  in 
1880,  when  Gill  proposed  his  regene- 
rative furnace.  He  constructed  two 
large  brick  chambers,  which  com- 
municated with  the  same  chimney 
so  that  while  one  was  burning,  the 
other  might  be  in  the  process  of 
charging.  The  combustion  here  could 
be  more  perfectly  regulated,  and  as 
these  chambers  had  a  double  bot- 
tom, thus  separating  the  ore  from  the 
collected  sulphur,  a  decided  advance 
was  made.  As  high  as  75  per  cent  of 
the  sulphur  was  obtained  by  this 
method. 

The  next  great  improvement  came 
in  1891,  when  the  removing  of  the 
sulphur  from  the  ore  was  effected  by 
the  use  of  superheated  steam.  This 
was  accomplished  by  building  hori- 
zontal iron  cylinders,  equipped  with 
a  tight-fitting  door  and  a  track  which 
would  allow  small  iron  cars,  with 
perforated  bottoms,  containing  the 
ore,  to  be  run  into  this  drum.  The 
door  is  closed  and  steam  at  130  deg. 
C.  admitted,  when  the  sulphur  melts, 
runs  to  the  bottom  of  the  drum, 
which  is  slightly  inclined,  and  then 
into  a  well  which  serves  as  a  recep- 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


73 


tacle  for  the  molten  sulphur.  This 
process  is  rapid,  gives  from  80  per 
cent  to  90  per  cent  of  the  total  sul- 
phur, and  does  away  with  the  objec- 
tionable sulphur  dioxide  fumes  of 
the  former  methods. 

All  of  these  methods  produce  crude 
sulphur  and  this  must  then  be  re- 
fined. This  refining  process  is  ac- 
complished by  heating  the  crude  sul- 
phur in  retorts  and  distilling  it  and 
condensing  it  in  large  chambers.  If 
the  temperature  of  these  condensing 
chambers  is  above  114  deg.  C.,  then 
liquid  sulphur  is  obtained,  which  is 
drawn  off  into  molds  and  known  as 
brimstone.  If  the  temperature  is 
maintained  below  100  deg.  C.,  then 
flowers  of  sulphur  will  collect. 

The  deposits  of  sulphur  in  Louisi- 
ana occur  about  1000  ft.  below  the 
surface  of  the  ground.  The  method 
of  obtaining  this  sulphur  was  sug- 
gested by  Frasch.  He  drilled  a  well, 
similar  to  that  used  for  extracting 
petroleum  from  the  earth,  then  into 
this  casing,  he  imposed  three  other 
concentric  tubes,  lined  with  alumi- 
num, which  would  not  be  attacked  by 
the  sulphur.  Superheated  water  was 
forced  down  through  the  outer  pipe. 
When  it  came  in  contact  with  the  sul- 
phur, the  latter  melted,  and  was 
forced  part  way  up  the  inner  tube. 

To  bring  it  the  remainder  of  the 
distance,  aluminum  pumps  were  tried 
but  were  not  strong  enough  to  sup- 
port the  strokes  of  the  piston.  The 
difficulty  was  then  overcome  by  forc- 
ing air  down  the  inner  tube  which 
emulsified  the  sulphur,  thus  making 
it  very  light  and  it  rose  to  the  sur- 
face. Here  it  was  collected  in  large 
wooden  boxes  where  it  solidified. 

By  simply  melting  this  sulphur 
again  in  iron  boilers  by  use  of  steam 
and  drawing  it  off  into  suitable 
molds,  a  sulphur  of  higher  than  97 
per  cent  is  obtained.  It  is  estimated 
that  the  Louisiana  deposits  contain 
at  least  forty  million  tons  of  sulphur. 

Sulphur  exists  in  three  forms. 
The  most  stable  is  the  rhombic 
variety  which  has  a  specific  gravity 
2.06  and  melts  at  114.5  deg.  C.  The 
monoclinic  is  next  in  stability  and 
has  a  specific  gravity  of  1.92.  Above 
95  deg.  C.,  the  rhombic  changes  into 


monoclinic  and  vice  versa.  If  boiling 
sulphur  at  a  temperature  of  445  deg. 
C.  is  poured  into  water,  there  re- 
sults a  form  devoid  of  crystalline 
structure  and  called  amorphous,  or 
plastic  sulphur.  It  resembles  rubber 
in  many  of  its  physical  properties 
but  soon  changes  back  into  the 
rhombic  variety.  Therefore  when 
sulphur  is  added  to  rubber  and  vul- 
canized at  45  Ibs.  pressure  of  steam 
that  is  equivalent  to  a  temperature 
of  145  deg.  C.  and  our  sulphur  must 
be  above  the  temperature  at  which 
rhombic  exists  and  in  fact  approach- 
ing the  temperature  at  which  the 
amorphous  exists. 

Rhombic  sulphur  exists  in  two 
modifications,  roll  sulphur  or  brim- 
stone and  flowers  or  flour  of  sulphur. 
It  is  the  latter  modification  which  is 
largely  used  in  the  rubber  industry. 
In  some  places,  they  grind  brim- 
stone, sift  it,  and  it  gives  equally  as 
good  results. 

The  flowers  of  sulphur  results  from 
the  sublimation  of  sulphur  as  was 
pointed  out  above.  Its  specific 
gravity  runs  about  2.0  and  it  con- 
tains some  modifications  which  are 
insoluble  in  carbon  bisulphide. 

It  always  contains  some  free  sul- 
phuric acid  due  to  its  slow  oxidation. 
The  sulphur  should  be  examined  from 
time  to  time  to  ascertain  the  amount, 
of  free  acid,  which  should  not  show 
more  than  0.2  per  cent  calculated  as 
H,S04.  It  should  contain  practically 
no  ash,  in  fact  the  presence  of  any 
suggests  adulteration,  generally  with 
an  infusorial  earth. 

Sulphur  is  sometimes  used  in  sul- 
phur baths  into  which  forms  to  be 
vulcanized  are  dipped,  and  here  it 
serves  simply  as  a  heat  carrier  in  the 
place  of  the  more  usual  steam  pres- 
sure or  hot  air.  . 

Sulphur  monochloride,  S2C1,,  was 
found  to  have  the  property  of  com- 
bining with  rubber  to  produce  a  sub- 
stance resembling  the  sulphur  vul- 
canized rubber.  It  has  the  power  of 
entering  into  this  chemical  union  at 
ordinary  temperature,  thus  we  have 
by  its  use  what  is  known  as  the  "  cold 
cure  "  process. 

It  is  made  by  passing  dry  chlorine 
gas  over  molten  sulphur,  when  the 


74 


RUBBER   MANUFACTURE 


two  elements  combine  in  the  ratio  of 
SoCl,.  It  distills  out  of  the  appa- 
ratus and  is  condensed  as  a  reddish 
yellow  liquid  with  a  boiling  point  of 
138  deg.  C  and  a  specific  gravity  of 
1.69.  Moisture  decomposes  it  in  the 
following  manner. 

2  S2C12  +  2  HOH  -> 
S02  +  3  S  +  4  HC1 

Therefore  when  it  is  used  in  the 
rubber  industry,  moisture  must  be 
excluded  as  far  as  possible. 

Sulphur  is  readily  soluble  in  the 
monochloride  and  the  monochloride 
is  likewise  converted  into  the  di- 
chloride  by  treating  it  with  an  excess 
of  chlorine.  So  when  examining  the 
monochloride,  we  necessarily  look  for 
these  two  substances,  sulphur  and 
sulphur  dichloride  as  impurities. 
The  presence  of  these  affects  the  boil- 
ing point  of  the  monochloride  and 
that  gives  us  a  very  easy  method  of 
ascertaining  the  relative  purity  of 
our  material.  In  commercial  work, 
a  range  in  boiling  point  from  130 
deg.  to  140  deg.  C  is  allowed. 

The  dichloride  has  a  boiling  point 
of  64  deg.  C,  and  it  is  a  very  ob- 
jectionable impurity  in  any  amount. 
The  dissolved  sulphur  may  run  as 
high  as  5  per  cent.  If  more  than  this 
is  present,  the  cured  article  will 
;'  bloom  "  or  "  sulphur  up."  This 
is  determined  by  distilling  off  the 
chloride  and  extracting  the  residue 
with  carbon  disulphide,  which  dis- 
solves the  sulphur,  placing  the  solu- 
tion in  a  tarred  flask,  evaporating 
the  solvent  off  and  drying  at  110  deg. 
C,  when  the  sulphur  remains  and  is 
determined. 

Pure  sulphur  chloride  should  con- 
tain 52.5  per  cent  of  chlorine.  It  is 
generally  used  for  vulcanizing  proc- 
esses in  a  dilute  solution  of  carbon 
bisulphide  or  carbon  tetrachloride 
and  the  articles  to  be  cured  are 
dipped  into  this  solution.  The  action 
is  only  'a  surface  action  and  there- 
fore may  be  used  only  with  thin 
articles.  In  some  cases  the  articles 
to  be  cured  are  subjected  to  the 
vapors  of  sulphur  chloride  when  the 
desired  reaction  takes  place  and  a 
glossy  surface  is  produced.  It  finds 
extensive  use  in  the  manufacture  of 


rubber  substitutes.  Its  use  here 
will  be  discussed  at  greater  length 
in  a  chapter  which  follows  and  which 
deals  entirely  with  the  question  of 
"substitutes." 

Because  of  the  use  of  carbon  bisul- 
phide and  carbon  tetrachloride  in 
the  "  cold  cure,"  it  seems  perhaps 
wise  to  devote  a  little  space  here  in 
considering  these  substances. 

Carbon  bisulphide,  like  the  chlor- 
ide of  sulphur,  is  made  by  the  direct 
union  of  the  elements.  The  appa- 
ratus for  effecting  this  action  con- 
sists of  a  tall,  heavy  walled  cast-iron 
retort  which  is  filled  with  carbon, 
generally  coke,  and  heated  to  red 
heat.  At  the  bottom  of  this  retort, 
there  enters  a  slow  stream  of  molten 
sulphur  which,  coming  into  the  re- 
tort, immediately  changes  into  vapor 
and  then  combines  with  the  carbon 
forming  the  bisulphide.  This  at  the 
temperature  of  the  retort  is  a  gas 
and  thus  passes  out  the  top  into  a 
system  of  condensers  which  first  re- 
move from  the  bisulphide  any  sul- 
phur vapors  which  may  have  been 
carried  along  with  it;  then  into  a 
water  condenser  which  condenses  the 
bisulphide. 

This  is  of  course  the  crude  product 
and  for  the  majority  of  cases  must 
be  purified.  This  is  done  by  adding 
to  it  a  little  lime  water  and  shaking 
it,  then  placing  it  in  a  still  with 
about  a  1  per  cent  solution  oil,  a  lit- 
tle water  and  some  lead  acetate. 
When  the  bisulphide  is  distilled  out, 
it  will  represent  a  fairly  good  grade. 

This  substance  is  used  very  exten- 
sively outside  the  rubber  industry. 
Up  to  1850,  however,  practically  its 
only  use  was  in  connection  with  the 
rubber  industry,  and  then  as  to-day 
it  was  used  as  a  diluent  in  the  cold 
cure  process,  and  as  a  solvent  for 
rubber,  hence  coming  its  use  in  the 
preparation  of  rubber  cements. 

It  boils  at  46  deg.  to  47  deg.  C, 
and  has  a  specific  gravity  of  1.27.  It 
generally  contains  some  dissolved 
sulphur,  which  may  be  determined 
by  distilling  100  c.c.  out  of  a  tared 
flask.  It  should  show  at  most  two 
grams  of  distillation  residue  per 
liter.  Having  such  a  low  boiling  point, 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


75 


it  evaporates  very  rapidly  and  with 
the  air,  forms  a  very  inflammable 
mixture  often  causing  bad  fires.  Its 
vapors  are  also  poisonous  and  may 
produce  serious  results  upon  the 
workmen.  The  tetrachloride  of  car- 
bon is  made  by  passing  dry  chlorine 
through  CS2  in  which  contains  a  little 
iodine  and  a  catalyst  of  asbestos  im- 
pregnated with  magnesium  chloride 
is  suspended.  The  reaction  takes 
place  as  follows : 

CS,  +  3  C12  ->  CC14  +  S2  C12 

These  two  products  may  be  sep- 
arated by  distillation,  but  it  has  been 
found  that  in  the  presence  of  a  little 
powdered  iron,  the  following  reac- 
tion will  take  place : 

CS,  +  2  S2  C12  >  CC14  +  6  S 

These  resulting  products  are  sep- 
arated by  distillation  and  the  sul- 
phur is  used  to  produce  carbon  bi- 
sulphide again. 

The  tetrachloride  is  purified  by 
washing  with  a  solution  of  caustic 
soda  and  then  distilling  from  a  so- 
lution of  calcium  hypochlorite.  It 
boils  at  77  deg.  C.  and  has  a  specific 
gravity  of  1.63.  It  is  an  excellent 
solvent  for  fats  and  resins  and  has 
the  great  advantage  of  not  being  in- 
flammable. It  even  has  the  power 
of  rendering  certain  inflammable 
solvents  uninflammable  when  it  is 
added  to  them.  Its  great  use  in  the 
rubber  industry  is  that  it  is  mixed 
with  coal  tai-  naphtha  and  will  pro- 
duce non-inflammable  rubber  solu- 
tions, and  likewise  its  use  as  a  dilu- 
ent in  the  cold  cure  process. 

To  test  the  commercial  variety  of 
the  tetrachloride,  it  should  distill  be- 
tween 75  deg.  and  78  deg.  C.  and 
leave  no  residue.  The  determina- 
tion of  its  specific  gravity  will  gen- 
erally reveal  the  presence  of  any 
adulterants. 

Inorganic  Accelerators 

The  second  group  of  materials  we 
called  inorganic  accelerators  or  ' '  sul- 
phur carriers  "  as  they  have  some- 
times been  called.  The  theories  ad- 
vanced in  explanation  of  their  action 
in  hastening  vulcanization  will  be  re- 
served for  the  chapter  dealing  with 
the  theories  of  vulcanization. 


The  one  which  has  been  used  to 
greatest  extent  is  probably  litharge, 
the  monoxide  of  lead.  It  is  made  by 
heating  the  metal  lead  in  a  reverber- 
atory  furnace  with  a  current  of  air 
passing  over  it.  It  requires  some 
time  for  the  oxidation  to  be  complete 
and  must  also  be  watched  that  some 
of  the  other  oxides  of  lead  are  not 
formed.  The  yellow  powder  formed 
in  the  above  process  is  called  Mas- 
sicot. When  this  is  melted  and  then 
allowed  to  cool  rapidly,  the  mass 
which  results  is  called  litharge.  It 
has  a  specific  gravity  of  from  9.2  to 
9.5.  Considerable  litharge  is  also 
made  to-day  in  connection  with  the 
refining  of  silver.  The  lead  is  re- 
moved from  the  molten  silver  when 
it  is  oxidized  with  a  current  of  air 
to  the  monoxide.  It  then  floats  on 
the  surface  of  the  silver  and  is  re- 
moved. 

Litharge  is  generally  supplied  in 
a  high  state  of  chemical  purity,  but 
varies  considerably  in  degree  of  fine- 
ness and  this  of  course  has  an  in- 
fluence upon  its  color.  Litharge  is 
slightly  basic  and  therefore  tends 
to  absorb  carbon  dioxide,  which  is  ob- 
jectionable. A  sample  should  there- 
fore dissolve  in  dilute  nitric  acid 
without  any  effervescence,  and  with- 
out leaving  a  residue  of  the  dark 
colored  lead  peroxide,  which  is  very 
objectionable. 

It  may  contain  some  unoxidized 
metal,  which  does  no  harm  and  may 
be  detected  by  dissolving  the  litharge 
in  acetic  acid  instead  of  nitric.  It 
is  always  well  to  test  the  resulting 
solution  for  copper  as  that  is  ob- 
jectionable even  in  small  amounts. 

Litharge  might  well  be  classed 
under  the  heading  of  Black  Pigments 
as  it  imparts  that  color  to  the  vul- 
canized rubber  due  to  the  forma- 
tion of  its  sulphide.  Until  recently, 
nearly  all  of  the  black  and  dark  gray 
rubbers  were  colored  with  litharge 
but  at  present  it  is  used  largely  on 
account  of  its  accelerating  action 
upon  vulcanization. 

White  lead  is  a  basic  carbonate  of 
lead  and  has  an  accelerating  action 
upon  the  rate  of  cure  but  to  a  less 
degree  than  litharge.  As  a  pigment, 
it  does  not  possess  the  coloring  power 


76 


RUBBER    MANUFACTURE 


which    litharge    has.      It    gives    the 
article  more  of  a  bluish  gray  color. 

It  is  made  by  several  different 
methods,  some  requiring  a  long 
period  of  time,  others  proceeding 
more  rapidly.  From  the  white 
lead  manufacturer's  point  of  view, 
the  rapid  method  is  naturally  the  one 
to  be  preferred,  but  from  the  con- 
sumer's viewpoint,  the  products  of 
the  slow  process  seem  to  be  desired 
most. 

The  Old  Dutch  Process  consists  in 
subjecting  lead  plates  to  the  action 
of  acetic  acid  and  carbon  dioxide 
formed  by  fermentation.  This  first 
produces  the  acetate  of  lead,  then  the 
basic  acetate,  and  finally  after  a  lapse 
of  five  or  six  weeks,  the  basic  car- 
bonate, a  white  lead,  results.  The 
white  lead  is  freed  from  any  un- 
affected lead  or  acetate  by  washing 
with  water.  The  Germans  have  a 
quicker  method  where  they  blow 
steam  and  acetic  acid  vapors  into 
chambers  containing  lead  plates  and 
then  bring  into  these  same  chambers 
carbon  dioxide  from  a  coke  furnace 
and  the  basic  carbonate  of  lead  re- 
sults. It  is  washed  and  dried,  and 
ready  for  market. 

The  French  dissolve  litharge  in 
acetic  acid  forming  the  basic  acetate 
and  then  pass  carbon  dioxide  through 
this  until  the  white  lead  formed, 
which  settles  to  the  bottom,  is  trans- 
ferred to  a  filter  press,  dried  and 
ground. 

The  Russian  white  lead  is  made  by 
producing  the  neutral  lead  carbon- 
ate by  the  action  of  carbon  dioxide 
upon  the  basic  acetate  of  lead.  The 
neutral  carbonate  is  then  made  into 
a  paste  with  water,  about  1  per  cent 
of  lead  acetate  added,  and  also  30 
per  cent  of  lead  oxide.  The  whole 
mass  is  stirred  in  the  cold  with  the 
addition  of  a  little  water  until  it  all 
hardens.  In  from  three  to  four 
hours,  the  process  is  complete  and  a 
fine  grade  of  white  lead  results. 

There  is  a  method  whereby  the 
freshly  precipitated  lead  sulphate  is 
converted  into  the  basic  sulphate  by 
heating  with  caustic  soda,  then  when 
this  solution  is  heated  with  sodium 
carbonate,  the  white  lead  is  pre- 


cipitated. In  this  country,  atomized 
lead  is  produced  by  blowing  a  jet  of 
steam  against  small  holes  where 
molten  lead  is  issuing.  This  "  lead 
sand  "  is  then  treated  with  dilute 
acetic  acid  for  about  seven  days, 
while  air,  carbon  dioxide,  and  a  little 
steam  are  blowing  through  the  vats. 
White  lead  results  which  is  washed 
from  the  unaltered  lead. 

The  water  of  hydration  which 
may  be  present  in  white  lead  often 
causes  "  blowing."  It  has  a  specific 
gravity  of  6.1  to  6.2. 

Sublimed  white  lead  is  not  what 
the  name  implies,  a  carbonate  of  lead, 
but  is  a  basic  sulphate.  Its  use  is  in- 
creasing in  favor  as  it  does  not  tend 
to  produce  "  blowing."  It  acceler- 
ates more  than  white  lead,  and  pro- 
duces a  black  product  when  vulcan- 
ized. It  is  a  velvety  powder  and 
mixes  readily  with  the  rubber.  It 
has  a  slightly  higher  density  than 
white  lead. 

Red  lead,  or  minium,  is  the  tetrox- 
ide   of  lead,   or  really    it    may    be 
thought  of  as  a  mixture  of  lead  mon- 
oxide and  dioxide. 
2  PbO  +  Pb(X  ->  Pb3  04  (Red  Lead) 

It  is  made  by  heating  litharge  in 
a  reverberatory  furnace  at  a  tem- 
perature of  450  deg.  C.,  but  must  not 
be  allowed  to  melt.  The  best  grade 
is  made  by  heating  the  monoxide  of 
lead  with  sodium  nitrate  in  an  oxidiz- 
ing flame  to  a  dark  red  heat.  It  has 
a  specific  gravity  of  8.0  to  9.  It  is 
one  of  the  most  powerful  inorganic 
accelerators,  perhaps  due  to  the  heat 
of  reaction  between  it  and  the  sul- 
phur. It  is  used  in  rapid  curing 
stocks.  It  can  be  used  only  within 
certain  limits  as  it  will  attack  the 
rubber  as  a  result  of  its  strong  oxidiz- 
ing power. 

The  adulterants  that  must  be 
looked  for  are  calcium  carbonate, 
barytes  and  ferric  oxide. 

Under  the  term  "  Lime,"  we 
largely,  in  connection  with  rubber, 
refer  to  the  hydroxide  of  calcium 
which  is  "  slaked  lime,"  in  contrast 
to  ' '  quick  "  or  "  burnt  lime  ' '  which 
is  the  oxide  of  calcium.  The  latter  is 
made  by  heating  limestone,  which 
is  calcium  carbonate,  in  kilns  to  a 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


77 


temperature  of  1,000  deg.  when  it 
loses  its  carbon  dioxide  and  quick 
lime  results.  When  this  is  mixed 
with  about  one-third  of  its  weight  of 
water,  the  white,  po\vdery,  swollen 
mass  of  slaked  lime  results.  If  more 
water  is  added,  the  soluble  alkalies 
are  washed  out  and  a  softer  powder 
will  result.  It  has  a  specific  gravity 
of  2.1  and  has  a  finer  grain  than 
the  quick  lime.  It  is  added  only  in 
small  proportions. 

In  small  quantities,  it  takes  up  the 
moisture  wrhich  may  be  present  in  a 
stock  and  thus  prevents  blowing.  It 
has  the  power  of  combining  with  the 
free  sulphur  and  thus  tends  to  pre- 
vent "  blooming."  Excess  of  lime 
tends  to  diminish  the  resiliency  of 
rubber  and  also  makes  it  harder,  hav- 
ing that  effect  even  in  hard  rubber 
articles.  It  also  has  an  accelerating 
action  upon  the  rate  of  cure. 

Lime  should  be  fairly  free  from 
carbonate  and  silica  and  upon  igni- 
tion show  close  limits  to  that  of 
Ca  (OH)2,  that  is,  24.3  per  cent. 
Manganese  is  sometimes  present  in 
lime  and  renders  it  useless  for  the 
rubber  manufacturer.  It  affects  rub- 
ber in  the  same  manner  as  copper 
does. 

There  are  several  forms  of  mag- 
nesium compounds  in  use.  We  have 
two  kinds  of  calcined  magnesia 
(which  is  the  oxide),  known  as 
"  heavy  "  and  "  light  "  calcined. 

If  to  a  hot  solution  of  a  mag- 
nesium salt,  a  hot  solution  of  soda 
is  added,  there  will  be  formed  what 
is  known  as  heavy  magnesium  car- 
bonate and  when  this  is  calcined,  the 
heavy  magnesia  results.  If,  on  the 
contrary,  cold  solutions  are  used,  the 
light  carbonate  will  be  formed,  and 
when  this  is  calcined  the  light  mag- 
nesia results.  The  only  difference 
therefore  is  in  the  structure  of  the 
two. 

It  is  used  in  the  same  manner  as 
lime.  Its  specific  gravity  is  3.2  to 
3.6  and  it  is  a  little  coarser  grained. 
It  possesses  marked  accelerating 
power  upon  the  rate  of  cure  and  also 
increases  the  toughness  of  the  prod- 
uct more  than  10  per  cent  except 
in  rapidly  curing  stocks. 


The  magnesias  suffer  varying  igni- 
tion losses  ranging  from  2  to  20  per 
cent.  When  a  compound  has  been 
made  up  with  a  certain  grade  of 
magnesia,  then  deliveries  which  fol- 
low should  not  be  allowed  to  vary 
much  from  the  ignition  loss  of  the 
original.  Rubbers  running  high  in 
resins  seem  to  give  better  results 
when  compounded  with  magnesia. 

There  occurs  in  nature  the  mineral, 
magnesite,  which  is  the  carbonate  of 
magnesium,  of  sufficient  purity  that 
it  may  be  used  in  compounding.  The 
carbonate  is  also  artificially  made  as 
pointed  out  above. 

These  substances  possess  very  little 
accelerating  power,  and  are  used 
largely  as  fillers.  As  fillers  they  may 
be  employed  up  to  30  per  cent  with- 
out seriously  injuring  the  rubber. 

Under  the  third  division  of  oui 
subject,  fillers  will  be  considered  in 
the  meaning  which  the  word  itself 
implies:  substances  which  are  not 
used  on  account  of  any  good  prop- 
erty which  they  impart  to  the  rubber, 
nor  on  account  of  any  color  which 
they  may  produce  in  the  finished  prod- 
uct. In  other  words,  they  are  cheap 
materials  which  to  a  certain  extent 
may  be  used  in  the  place  of  more  ex- 
pensive substances.  Their  amount  is 
regulated  by  experiment  so  that  too 
much  will  not  be  used  and  thus  im- 
pair the  finished  product. 
Barytes 

The  first  one  of  these  for  considera- 
tion will  be  barytes,  or  heavy  spar. 
It  is  found  in  nature  in  a  compara- 
tively pure  form,  in  fact,  in  so  high 
a  degree  of  purity  that  it  needs  no 
other  preparation  than  that  of  grind- 
ing to  a  fine  powder.  It  may  be 
found  in  shades  varying  from  a  good 
white  to  a  gray,  depending  upon  the 
per  cent  of  barium  sulphate  present. 

It  is  obtained  also  by  artificial 
means.  First,  the  mineral  or  natural 
sulphate  is  heated  in  a  furnace  with 
carbon  when  there  results  the  sul- 
phide and  oxide  of  barium.  These 
are  then  dissolved  in  water  and  so- 
dium sulphate  added  and  the  insolu- 
ble artificial  barium  sulphate,  barytes, 
is  precipitated. 

Second,   it  is   made  by  dissolving 


78 


RUBBER    MANUFACTURE 


the  mineral  erite.  which  is  the  car- 
bonate of  barium,  in  hydrochloric 
acid,  and  then  adding  sodium  sul- 
phate, when  the  barium  sulphate  re- 
sults. 

It  has  a  specific  gravity  of  4.5  to 
4.6  and  is  obtained  very  often  under 
the  name  of  "  permanent  white  "  or 
:<  blanc  fixe."  Due  to  its  high  spe- 
cific gravity,  it  is  employed  to  in- 
crease the  specific  gravity  of  some 
stocks.  The  artificial  product  is  to  be 
preferred  to  the  natural  one  as  it  is 
amorphous  while  the  ground  mineral, 
even  though  it  is  reduced  to  a  fine 
powder,  still  retains  more  or  less  its 
crystalline  structure.  It  is  used  to 
adulterate  white  lead,  and  to  a  cer- 
tain extent,  has  the  advantage  of  not 
being  effected  by  hydrogen  sulphide 
or  metallic  sulphides. 

Aluminum  Compounds 

There  are  several  compounds  of 
aluminum  which  are  used  as  inert 
fillers. 

"  Aluminum  flake  "  is  a  natural 
product  coming  in  several  different 
colors  from  white  to  gray  and  gray  to 
brown.  It  has  a  specific  gravity  of 
2.5  to  2.6  and  is  used  to  a  certain  ex- 
tent in  place  of  zinc  oxide. 

Aluminum  oxide  does  occur  in  na- 
ture but  the  artificial  product  is  the 
one  desired  for  use  in  rubber.  In  the 
Bayer  process  the  mineral  bauxite 
is  calcined  and  pulverized,  mixed 
with  a  little  lime  and  then  treated 
with  sodium  hydroxide  solution  of  45 
de.  Be,  at  a  pressure  of  three  to  four 
atmospheres.  Sodium  aluminate  re- 
sults which  is  soluble  in  water.  It  is 
then  filtered  hot  and,  after  suitable 
dilution,  pure  gelatinous  aluminum 
hydroxide  is  added.  It  is  then  agi- 
tated for  from  five  to  six  days  when 
all  of  the  aluminum  is  precipitated 
both  from  the  bauxite  solution  and 
from  that  which  was  added.  It  is 
then  recovered  by  a  filter  press,  and 
thoroughly  dried,  when  a  fine  white 
powder  results  with  a  specific  gravity 
of  about  3.9.  It  was  with  the  use 
of  this  oxide  that  Eaton  suggested  the 
making  of  a  pure  white  rubber. 

The  hydroxide  of  alumina  is  now 
coming  into  use  in  some  factories.  It 
is  one  of  the  lightest  gravity  materials 
possible  to  obtain. 


Kaolin,  or  China  clay,  is  a  natural 
occurring  product.  In  chemical  com- 
position it  is  a  hydrated  silicate  of 
alumina.  It  acts  as  an  inert  filler  in 
all  the  rubber  compounds.  It  has  a 
specific  gravity  of  2.3  to  2.6.  It 
should  show  an  ignition  loss  of  11  to 
14  per  cent  and  should  not  be  at- 
tacked by  dilute  acids.  It  often  runs 
very  high  in  moisture  which,  of 
course,  must  be  guarded  against. 

Talc 

Talc  is  a  silicate  of  magnesia  oc- 
curring native  in  the  earth  in  a  suffi- 
ciently high  state  of  purity  so  that  it 
may  be  reduced  to  a  powder  and  used 
directly  in  the  industries.  It  is  not 
used  to  any  great  extent  in  rubber 
stocks  but  is  employed  a  great  deal 
in  all  kinds  of  work  to  prevent  sur- 
faces from  sticking  together.  Molds 
are  dusted  over  with  it  to  keep  the 
rubber  from  adhering  to  them  dur- 
ing vulcanization.  Some  goods  are 
buried  in  it  during  vulcanization. 

Talc  has  a  specific  gravity  of  2.7. 
When  it  is  used  in  compounding,  it 
imparts  to  the  rubber,  smoothness 
and  stiffness,  and  also  increases  elec- 
trical insulation  when  used  in  cable 
coverings.  A  common  adulterant  is 
calcium  carbonate,  which  is  detected 
by  the  effervescence  when  treated 
with  an  acid. 

Saapstone  is  really  a  form  of  talc 
and  as  such,  is  used  in  large  quanti- 
ties. 

Silicon  Oxides 

There  are  other  materials  on  the 
market  under  different  names  which 
are  in  reality  the  same  from  a  chem- 
ical point  of  view.  Silica,  Atmoid, 
Infusorial  Earth,  Fossil  Flour  and 
Mountain  Flour  are  all  names  given 
to  the  oxide  of  silicon.  This  mate- 
rial occurs  in  a  great  many  different 
forms  in  nature.  All  forms  are  with- 
out material  effect  upon  rubber  com- 
pounds, other  than  stiffening  the 
product  to  some  extent.  They  have 
a  low  specific  gravity  ranging  between 
2.7  and  2.9. 

These  materials  consist  of  the  skele- 
tons of  microscopic  animals.  Large 
deposits  are  found  in  Nova  Scotia 
and  Germany. 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


79 


Asbestos 

Asbestos  is  a  silicate  of  magnesia 
with  a  varying  amount  of  the  mag- 
nesia replaced  by  lime,  together  with 
ferrous  oxide  and  alumina.  Large 
deposits  of  it  are  found  in  Italy, 
Canada  and  Cape  of  Good  Hope.  It 
is  used  both  as  fiber  and  as  powder. 
The  fibrous  form  is  used  in  mechan- 
ical goods  for  it  increases  the  tough- 
ness and  unyielding  quality  of  the 
structure.  It  is  used  in  goods  that 
are  subjected  to  a  high  temperature 
and  also  in  articles  like  brake  blocks. 

Calcium  Carbonates 

Chalk  or  whiting  is  the  carbonate 
of  calcium.  It  occurs  in  nature  in 
several  modifications,  as  limestone, 
chalk,  and  marble.  The  chalk  deposits 
are  the  remains  of  microscopic 
marine  animals.  Chalk  is  obtained 
in  a  fine  white  grade. 

Whiting  is  really  purified  chalk, 
made  by  grinding  the  chalk,  then 
floating  it  and  the  fine  white  sediment 
is  obtained  by  running  it  through  a 
filter  press.  It  is  then  dried  rapidly. 
If,  during  the  drying,  too  high  a  tem- 
perature is  used,  the  product  will 
feel  harsh.  As  it  is  slightly  deliques- 
cent it  must  be  kept  in  a  dry  place; 
otherwise  it  may  cause  trouble  in  the 
stock  where  it  is  used. 

Large  quantities  of  whiting  are 
used  in  the  rubber  business  on  ac- 
count of  its  cheapness.  It  has  a  spe- 
cific gravity  of  2.7  to  2.9.  It  will 
increase  the  resiliency  of  rubber  and 
also  increase  its  hardness  without 
producing  the  "  stony  "  effect  that 
other  ingredients  do. 

Sulphides 

We  find  in  nature  mineral  deposits 
of  the  two  sulphides  of  lead  and  zinc. 
If  such  ore  is  smelted  with  a  mixture 
of  coal  and  lime,  it  produces  what  is 
known  as  Blue  Lead.  It  is  an  ex- 
tremely fine  pOAvder  and  possesses  a 
high  specific  gravity.  It  is  a  cheap 
product  and,  to  a  certain  degree,  hast- 
ens the  rate  of  cure  in  the  stocks 
where  it  is  used.  Therefore,  it  may 
be  used  in  the  place  of  litharge  and 
will  also  produce  the  fine  black  prod- 
uct. 

Magnesium  Carbonate 
Magnesium   carbonate,   which   was 


mentioned  under  the  first  class,  is  also 
used  as  a  filler. 

White  Pigment 

Under  our  third  group,  White 
Pigments,  may  be  discussed  materials 
which  might  have  been  grouped 
under  fillers.  This  will  be  true  of  all 
the  divisions  which  follow. 

Zinc  Oxide 

The  first  and  most  important  of  the 
white  pigments  is  zinc  oxide.  No  one 
pigment  is  used  as  extensively  as  this 
one  in  the  manufacture  of  white  rub- 
ber goods. 

It  may  be  made  by  roasting  any  one 
of  the  zinc  ores,  but  the  best  method 
is  that  of  burning  the  pure  metal.  The 
trouble  with  roasting  the  ores  lies  in 
the  fact  that  lead,  iron,  and  copper 
are  very  often  present  in  these  and 
thus  will  be  found  in  the  finished 
product. 

A  good  sample  of  zinc  oxide  should 
dissolve  completely  without  effervesc- 
ing in  a  10  per  cent  solution  of  acetic 
acid.  If  it  is  desired  to  test  for  the 
presence  of  iron,  lead  or  copper,  in 
the  oxide,  all  that  is  necessary  to  do 
is  to  dissolve  the  specimen  in  dilute 
hydrochloric  acid,  and  conduct  hy- 
drogen sulphide  into  it.  If  it  is  free 
from  the  above  metals,  there  will  be 
no  preciptate  formed. 

Inferior  grades  of  zinc  are  often 
adulterated  with  barytes,  whiting,  or 
kaolin  and  the  presence  of  these  will 
be  detected  when  the  sample  is 
treated  with  acetic  acid.  The  barytes 
and  kaolin  are  both  insoluble  and  the 
whiting  will  produce  the  effervesc- 
ence. White  lead  is  sometimes  an 
adulterant. 

Zinc  oxide  has  a  specific  gravity  of 
5.5  to  5.6.  Although  it  is  one  of  the 
extensively  used  white  pigments,  yet 
it  is  not  all  that  is  to  be  desired.  Its 
covering  power  is  only  moderate  and 
during  vulcanization,  it  turns  to  a 
yellow  color.  The  higher  the  tem- 
perature and  longer  the  period  of 
vulcanization,  the  more  pronounced 
this  color  becomes. 

Another  defect  of  zinc  oxide  is  the 
fact  that  dilute  acids  will  dissolve  it 
out  of  the  vulcanized  rubber  goods. 
As  a  result  of  this,  certain  countries 
prohibit  its  use  in  rubber  articles 


80 


RUBBER   MANUFACTURE 


which  come  in  contact  with  foods  or 
beverages  in  their  preparation. 

Zinc  Sulphide 

A  white  pigment  which  has  in- 
creased in  favor  rapidly  is  zinc  sul- 
phide. It  occurs  in  nature  in  the 
mineral  known  as  zinc  blende,  but 
the  product  used  in  rubber  is  an  arti- 
ficial one.  It  may  be  produced  by 
causing  zinc  dust  and  vapors  of  sul- 
phur to  come  together  at  an  elevated 
temperature.  It  may  also  be  pro- 
duced by  precipitating  it  from  a  solu- 
tion of  zinc  with  ammonium  sulphide. 

It  is  a  white  powder  with  a  specific 
gravity  of  3.3  and  possesses  greater 
covering  power  than  the  oxide.  It 
has  the  distinct  advantage  of  not 
changing  to  the  yellow  tint  during 
vulcanization,  and  it  is  not  leached 
out  of  the  rubber  by  dilute  acids  as  is 
the  oxide.  It  is  liable  to  the  same 
adulterations  as  the  oxide  is  plus  the 
oxide  itself.  The  best  grades  of  zinc 
sulphide  should  run  as  high  as  90 
per  cent,  purity. 

A  very  good  method  of  determining 
its  purity  is  to  place  about  0.2  of  a  gram 
of  the  dried  material  in  a  flask  and 
shake  it  up  with  50  c.c.  of  N/10  iodine 
solution.  Five  c.c.  of  concentrated 
hydrochloric  acid  are  then  added  and 
the  whole  is  allowed  to  stand  a  couple 
of  hours  with  occasional  shaking. 
By  this  time,  all  of  the  white  par- 
ticles should  have  disappeared  and 
the  excess  iodine  is  then  titrated  with 
sodium  thiosulphate  solution.  Each 
c.c.  of  the  iodine  solution  which  re- 
acted with  the  hydrogen  sulphide, 
produced  when  the  acid  was  added  to 
the  zinc  sulphide,  is  equivalent  to 
0.00485  grams  of  the  sulphide.  Thus 
its  purity  is  easily  calculated. 

Lithopone 

Another  zinc  pigment  which  was 
first  used  in  paint  and  now  exten- 
sively in  rubber,  is  one  known  as 
lithopone.  It  is  an  artificial  prod- 
uct, made  by  bringing  together  solu- 
tions of  barium  sulphide  and  zinc  sul- 
phate, when  the  following  reaction 
takes  place  : 


Ba  S  4-  Zn  S04  -*>Ba  804 

The    resulting    product    is    insol- 
uble and  is  a  compound  of  zinc  sul- 


phide and  barium  sulphate  which  is 
known  as  lithopone.  It  has  a  specific 
gravity  of  3.8  to  4.2  and  should  con- 
tain 70.5  per  cent  of  barium  sulphate 
and  29.5  per  cent  of  zinc  sulphide.  It 
varies  considerably,  however,  from 
these  per  cents,  depending  upon  the 
method  of  preparation. 

Of  course,  the  valuable  part  of  it 
is  due  to  the  zinc  sulphide  and  there 
is  a  standard  grade  of  lithopone, 
known  as  "  Blue  Seal,"  which  is 
guaranteed  to  have  30  per  cent  of 
zinc  sulphide.  For  general  purposes 
it  is  necessary  only  to  examine  a  sam- 
ple for  moisture,  acid  insoluble,  and 
sulphide. 

The  acid  insoluble  is  determined  by 
boiling  one  gram  of  the  dried  sample 
with  concentrated  hydrochloric  acid, 
diluting  and  boiling  again  and  then 
filtering,  drying  and  igniting  the 
residue  in  a  platinum  crucible,  and 
then  weighing.  This  residue  should 
not  exceed  70  per  cent. 

To  detect  the  presence  of  kaolin  as 
an  adulterant,  a  little  hydrofluoric 
acid  may  be  added  to  the  residue, 
evaporated  off,  and  reweighed,  and 
any  loss  in  weight  represents  the 
presence  of  silicates. 

What  was  said  in  regard  to  the  use 
of  zinc  sulphide  may  be  said  of  litho- 
pone. 

Rarytes  and  Kaolin 

In  addition  to  these  white  pig- 
ments, may  be  mentioned  barytes  and 
kaolin,  which  were  considered  under 
fillers. 

Red  Pigments 

The  next  class  of  pigments  for  our 
consideration  are  those  which  impart 
a  red  color  to  rubber  goods. 

Golden   and   Crimson   Antimony 

The  first  to  be  mentioned  are  Anti- 
mony Grolden  and  Crimson,  and  these 
two  are  divided  into  grades  accord- 
ing to  color,  for  instance,  Golden 
No.  1,  Golden  No.  2. 

The  Crimson  Antimony  is  little 
used  by  itself  but  is  made  by  boiling 
together  antimony  trichloride  and 
thiosulphate  solutions,  when  the  tri- 
sulphide  of  antimony  is  precipitated. 

Colors  varying  from  this  crimson 
to  orange  are  then  produced,  the 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


81 


shade  depending  upon  the  conditions 
of  precipitation  or  upon  the-  respec- 
tive percentages  of  crimson  and 
golden  sulphides  in  the  mixtures. 

The  golden  sulphides  are  the  ones 
in  commonest  use.  These  are  made 
by  boiling  powdered  stribnite,  which 
is  the  mineral  containing  the  natural 
sulphide  of  antimony,  with  alkaline 
polysulphides  when  there  results  sulf- 
antimonate  in  solution.  When  this 
sulfantimonate  is  treated  with  hydro- 
chloric acid  there  will  be  precipitated 
a  mixture  of  the  sulphides  of  anti- 
mony and  also  some  free  sulphur  re- 
sulting from  the  polysulphides. 

One  form  of  the  orange  antimony 
is  co-precipitated  with  hydrated  cal- 
cium sulphate  and  is  called  "  plas- 
tered antimony.''  This  grade,  of 
course,  is  cheaper  and  does  not  con- 
tain as  high  a  percentage  of  the  red 
pigment. 

When  it  comes  to  determining  the 
true  worth  of  a  sample  of  antimony, 
the  best  method  is  to  subject  it  to 
actual  vulcanization  experiments,  be- 
cause it  is  found  that  some  antimonies 
will  not  hold  their  color  during  vul- 
canization. This  fact  cannot  be  ascer- 
tained by  chemical  tests. 

In  analysis  the  following  deter- 
minations are  generally  made :  mois- 
ture, free  sulphur,  antimony,  calcium 
sulphate,  sulphide-sulphur. 

The  free  sulphur  present  is  what 
led  many  to  believe  for  a  long  time 
that  antimony  red  was  a  vulcanizing 
agent.  In  fact,  even  now  some  manu- 
facturers claim  that  they  obtain  bet- 
ter results  if  they  mix  the  sulphur 
into  the  antimony  which  they  use  in 
the  compound.  To  supply  such  a  de- 
mand the  producers  of  sulphureted 
antimony  put  free  sulphur  into  it  up 
to  the  extent  in  certain  cases  of  40 
per  cent.  It  is  determined  by  extract- 
ing a  weighed  amount  of  antimony  in 
a  Soxhlet  extractor  with  carbon  disul- 
phide  or  acetone  for  about  eight 
hours.  The  solvent  is  evaporated  and 
the  amount  of  free  sulphur  calcu- 
lated. 

The  antimony  itself,  iron  and  cal- 
cium sulphate  are  determined  in  the 
usual  manner.  The  sulphide  sulphur 
is  calculated  by  determining  the  total 
sulphur  in  the  extracted  sample  and 


subtracting    from    this    the    sulphur 
present  in  the  sulphate. 

In  connection  with  the  use  of  the. 
sulphides  of  antimony,  we  shall  pub- 
lish some  of  its  merits  as  put  forth 
by  a  prominent  manufacturer : 

"  First — Antimony  Sulphuret  used  in 
the  curing  of  rubber  nets  as  n  sulphur 
carrier  causing  all  of  its  free  sulphur  to 
unite  with  the  rubber.  Sulphur  added  as 
a  sulphnret  is  taken  up  completely  by  the 
rubber.  Therefore  it  is  not  necessary  to 
add  an  excess  of  sulphur. 

"  Second — On  account  of  the  above. 
'  blooming '  does  not  take  place  for  prac- 
tically none  of  the  sulphur  is  left  uncom- 
bined  in  the  rubber. 

"  Third — On  account  of  the  above,  vul- 
canization can  be  carried  on  at  a  lower 
temperature;  thus  the  tendency  to  over- 
cure  is  diminished. 

"Fourth — On  account  of  the  above,  the 
rubber  has  a  longer  life.  It  can  be  kept 
much  longer  than  gray,  rubber  before  it 
will  begin  to  deteriorate. 

"Fifth — It  has  more  elasticity.  This  is 
shown  by  the  following  test:  A  piece  of 
red  rubber  tubing  and  a  piece  of  gray 
tubing  are  bent  firmly  and  pressed  with  a 
spring  clothespin  clip.  The  two  samples 
are  allowed  to  stand  in  the  sunlight  for 
several  days  when  the  clips  are  removed. 
It  will  be  noted  that  the  properly  anti- 
mony-cured red  tube  will  spring  back  into 
its  original  shape  immediately  upon  re- 
moval of  the  clamp.  The  gray  tube  goes 
back  into  its  old  form  slowly.  In  use  this 
is  noticed  when  a  tire  goes  flat  over  night. 
The  red  tube  allowed  to  bend  by  the 
weight  of  the  car  will  immediately  spring 
back  into  place  when  the  weight  is  re- 
moved. The  gray  tube  will  remain  bent 
even  after  the  weight  of  the  car  is  lifted. 

"  In  a  large  lot  of  returned  shelf  goods, 
half  gray  and  half  red.  the  following  was 
noticed.  The  gray  tubes  when  removed 
from  the  cartons  were  in  bad  shape.  They 
could  not  very  well  be  unfolded  as  their 
creases  seemed  to  be  permanent.  The  red 
ones,  however,  were  in  just  as  good  shape 
as  the  day  when  they  left  the  plant  more 
than  a  year  before  and  they  were  simply 
transferred  to  new  cartons  and  placed  on 
sale.  The  gray  tubes  were  covered  over 
with  a  thick  coating  of  sulphur  bloom 
while  the  red  ones  were  entirely  free  from 
bloom.  The  superintendent  of  the  plant 
pointed  out  the  fact  that  the  only  differ- 
ence between  the  two  -stocks  was  that  the 
gray  ones  had  obtained  all  of  their  sul- 
phur from  sulphur  flour  while  the  red 
ones  obtained  the  larger  part  of  ttheir  sul- 
phur from  antimony  sulphuret."' 

Due  to  the  oxidization  of  the  sul- 
phur. \ve  find  that  most  samples  con- 
tain free  sulphuric  acid.  The  amount 
should  iiever  exceed  0.06  per  cent. 


82 


Iron  Sesquioxide 

There  are  several  terms  used  for 
practically  the  same  ingredient,  the 
sesquioxide  of  iron.  We  see  it  sold  as 
rouge,  red  ochre,  Venetian  red,  red 
hematite  and  under  a  few  other 
names.  In  general  use  they  are  all 
inferior  to  the  antimony  colors,  but 
they  are  useful  in  the  manufacture  of 
non-poisonous  articles  and  hard  rub- 
ber, where  it  behaves  better  than  the 
antimony. 

Rouge 

Rouge  is  made  by  calcining  the  sul- 
phate of  iron  and  if  this  is  done  in 
the  presence  of  barium  or  calcium 
sulphates,  a  more  brilliant  color  is  ob- 
tained. It  has  a  specific  gravity  of 
5.0  to  5.2. 

Red  Ochre 

Red  ochre  is  made  by  heating  yel- 
low ochre,  which  is  a  clay  containing 
siliceous  matter  along  with  a  hydrated 
iron  oxide.  So  the  red  ochre  is  really 
a  rouge  diluted  with  a  siliceous  mat- 
ter and  is  consequently  of  less  value 
than  the  rouge. 

Red  Hematite 

Red  hemitate  is  the  mineral  fer- 
ric oxide  and  is  of  sufficient  purity 
and  of  such  a  color  that  it  is  used  as 
a  red  pigment  in  ebonite  and  articles 
that  must  be  heat-resisting. 

Venetian  red  and  indian  red  are 
artificial  ferric  oxide. 

Vermilion 

Vermilion  is  a  sulphide  of  mercury 
and  is  the  most  brilliant  of  all  red 
pigments,  likewise  the  most  expensive, 
therefore,  not  used  so  extensively.  It 
is  employed  in  dental  rubbers  and 
must  be  free  from  all  soluble  mercury 
salts. 

It  occurs  in  nature  as  the  mineral 
cinnabar.  It  is  produced  artificially 
by  heating  the  black  sulphide  in  a 
covered  cast-iron  pot  and  the  cinna- 
bar will  be  sublimed.  This  is  often 
purified  still  further. 

It  is  adulterated  with  iron  oxide, 
red  lead  and  sometimes  gypsum.  Its 
purity  is  easily  tested  by  heating  some 
in  a  porcelain  dish.  If  no  adulterant 
is  present  it  will  completely  vola- 
tilize, leaving  no  residue. 


Black  Pigments 

Under  black  pigments  occur  large- 
ly different  grades  of  carbon,  the  com- 
monest being  lampblack. 

Lampblack 

This  is  made  by  collecting  the  car- 
bon which  results  from  the  incom- 
plete combustion  of  oils,  fats,  resins, 
coal  and  like  organic  bodies.  As  a  re- 
sult of  the  varied  starting  out  ma- 
terials, we  naturally  get  varying 
grades  of  lampblack.  It  generally 
contains  some  greasy  materials  and 
the  amount  of  these  present  should  be 
determined  by  an  acetone  extraction. 

Lampblack  should  not  show  more 
than  5  per  cent  of  grease  and  should 
leave  practically  no  ash.  Lampblack 
has  a  specific  gravity  of  1.8  and  has 
come  into  extensive  use  just  recently. 

A  short  time  ago  it  was  used  only 
in  boots,  shoes,  carriage  cloth,  and 
druggist  supplies  but  today  it  is  one 
of  the  important  ingredients  used  in 
a  large  number  of  mechanical  goods 
and  extensively  in  tire  stock,  where  it 
appreciably  increases  the  strength  of 
the  stock  as  well  as  its  wearing  sur- 
face. 

Bone  Black 

Bone  black  is  obtained  by  calcin- 
ing defatted  bones  in  closed  vessels 
out  of  contact  with  air.  This  grade  of 
carbon,  therefore,  runs  very  high  in 
mineral  matter,  very  often  equaling 
90  per  cent  of  the  whole.  It  is  coarse 
and  harsh,  even  after  grinding,  and, 
although  a  black  pigment,  finds  only 
limited  use. 

Gas  Carbon 

Gas  carbon  is  a  pure  grade  of 
lampblack  which  is  quite  popular 
with  certain  manufacturers  at  pres- 
ent. 

Black  Hypo 

Black  hypo  is  a  pigment  which  has 
been  used  in  the  past  to  some  extent 
but  is  received  with  less  favor  at 
present.  It  is  made  by  heating  to- 
gether a  mixture  of  litharge,  sulphur 
and  lampblack.  The  composition  of 
the  resulting  product  is  uncertain.  It 
contains  some  lead  sulphide,  a  little 
free  sulphur  and  some  of  the  lead 
salts  of  oxygen  sulphur  acids.  It 
has  been  made  by  adding  sodium 
thiosulphate  to  a  solution  of  sugar 


THE  MANUFACTURE  AND  USE  OF  INORGANIC  FILLERS 


83 


of  lead,  when  lead  thiosulphate  is  pre- 
cipitated, and  is  sold  as  white  hypo. 
If,  however,  this  is  heated,  it  changes 
to  black,  due  to  the  formation  of  the 
sulphide.  During  the  vulcanization 
process,  if  white  hypo  has  been  used, 
it  will  suffer  the  same  change  and  pro- 
duce a  black  rubber.  Its  use  at  pres- 
ent is  waning. 

Graphite 

Graphite  is  a  form  of  carbon  oc- 
curring in  the  free  state  in  a  high 
degree  of  purity  and  is  also  an  arti- 
ficial product  today.  It  is  made  in 
electrical  furnaces,  where  coal  is  sub- 
jected to  a  very  high  temperature 
for  a  period  of  twenty-four  hours. 

Graphite  is  used  in  rubber  goods 
more  as  a  filler  perhaps  than  as  a 
pigment.  Its  coloring  power  is  not 
veiy  great.  It  will  stiffen  rubber  ar- 
ticles and  has  remarkable  lubricating 
properties,  preventing  the  rubber 
from  sticking  to  metals.  It  is  used 
in  the  compounding  of  steam  joint- 
ings and  goods  that  are  going  to  be 
subjected  to  a  high  temperature. 

Lead  Sulphide 

Lead  sulphide  is  also  used  as  a  black 
pigment,  whether  it  is  added  as  such 
or  in  the  form  of  some  other  lead  salt 
which  changes  into  the  sulphide  dur- 
ing vulcanization.  It  is  the  most 
abundant  form  of  lead  found  in 
nature  as  galena. 

Yellow  Pigments 

Now  we  will  mention  some  of  the 
common  yellow  pigments. 

Yelloiv  Ochre 

Just  as  we  had  a  red  ochre  so  there 
is  a  yellow  ochre.  The  red  variety 
is  the  pure  ferric  oxide,  but  if  this 
is  mixed  with  clay  or  siliceous  mat- 
ter, it  loses  its  red  color  and  vary- 
ing shades  of  orange  and  yellow 
result.  It  is  a  natural  occurring  prod- 
uct and  is  inert  in  rubber.  It  is  very 
cheap  and  the  color  it  produces  in 
rubber  lacks  brilliancy. 

Chrome  Yellow 

Chrome  yellow  is  the  chromate  of 
lead  and  is  made  by  adding  a  solution 
of  sodium  chromate  to  a  solution  of 
lead  acetate,  when  the  yellow  precipi- 
tate is  produced.  It  finds  extensive 


use  in  the  manufacture  of  toys  and 
cold  cured  goods,  where  its  lead  con- 
tent does  not  interfere. 

C-admium  Yellow 

Cadmium  yellow,  which  is  the  sul- 
phide of  the  metal,  is  one  of  the  best 
yellow  pigments.  It  is  made  by  pass- 
ing hydrogen  sulphide  into  a  solu- 
tion of  a  soluble  cadmium  salt.  It 
gives  to  rubber  a  fine  yellow  color 
and  is  not  affected  by  vulcanization. 
It  may  be  used  in  toys  as  it  is  non- 
poisonous.  The  cost  of  this  material 
has  practically  eliminated  its  use. 

Arsenic  Trisulphide 

Arsenic  trisulphide  is  an  excel- 
lent yellow  pigment  as  it  is  not 
affected  by  vulcanization,  but  it  is  so 
extremely  poisonous  that  its  use  has 
been  almost  abandoned.  When  it  is 
mixed  with  a  small  amount  of  zinc 
oxide,  it  will  produce  a  beautiful 
cream  colored  yellow. 

Yellow  Dyestuffs  Used 

The  yellow  colors  are  found  large- 
ly, however,  in  toys,  surgicals  and 
tilings,  and  beside  the  pigments  men- 
tioned above,  to-day  we  find  large 
quantities  of  organic  dyestuffs  being 
used  instead  of  the  mineral  pigments. 

Green  and  Blue  Pigments 

Green  and  blue  pigments  are  used 
in  the  same  line  of  goods  as  the  yel- 
low ones,  and  they  too  are  being  re- 
placed by  the  organic  dyestuffs.  A 
few  of  each,  however,  are  still  im- 
portant enough  to  be  mentioned. 

Chrome  Green 

Chrome  green  is  the  sesquioxide  of 
chromium.  It  is  made  by  melting 
together  one  part  of  potassium 
dichromate  and  three  parts  of  boric 
acid,  then  dissolving  out  the  potas- 
sium borate,  when  there  will  remain 
the  beautiful  green  powder.  It  is 
inert  in  rubber  and  is  not  affected  by 
vulcanization. 

Rinmann's  Green 

Einmann's  green  is  made  in  al- 
most any  shade  of  green  desired. 
Chemically  it  is  zinc  cobalt  oxide 
and  by  varying  the  two  metals,  dif- 
ferent shades  are  produced.  It  is 
made  by  calcining  the  precipitate 


84 


RUBBER   MANUFACTURE 


formed  when  a  solution  of  sodium 
carbonate  is  added  to  a  solution  con- 
taining the  sulphates  of  zinc  and  co- 
balt. It  gives  a  fairly  good  green 
color  in  cold  cured  goods. 

Ultramarines 

On  the  border  line  between  the 
green  and  blue  pigments,  we  find  the 
very  interesting  substance  known  as 
ultramarine,  existing  as  a  green  pig- 
ment or  a  blue  one  depending  on  its 
method  of  preparation. 

No  one  knows  to  what  it  owes  its 
color.  It  is  made  by  heating  to  bright 
redness  in  a  covered  crucible  for 
three  or  four  hours  an  intimate  mix- 
ture of  100  parts  of  pure  kaolin,  100 
of  dried  sodium  carbonate,  60  of  sul- 
phur and  12  of  charcoal.  Chemically 
we  should  expect  such  a  mixture  to 
give  the  silicate  of  sodium,  the  alumi- 
nate  of  sodium,  and  sodium  sulphide, 
which  might  give  the  whole  mixture  a 
brown  color,  but  on  the  contrary  the 
mass  is  green  and  is  known  as  ultra- 
marine green.  It  is  a  permanent 
color  and  is  used  as  an  inert  pigment. 

If  this  green  is  powdered,  washed 
with  water  and  dried,  then  mixed 
with  one-fifth  of  its  weight  of  sul- 
phur and  gently  roasted  until 
the  sulphur  is  removed,  and  this  re- 
peated again  perhaps  if  necessary, 
the  residue  will  possess  a  beautiful 
blue  color  and  as  such  is  known  as 
ultramarine  blue.  This  is  used  in 


the     production      of     blue      rubber 
articles,  tiling,  etc. 

Acids  have  the  power  of  destroy- 
ing both  the  green  and  the  blue  color 
of  these  ultramarines. 

Prussian  Blue 

Prussian  blue  is  made  by  adding 
a  solution  of  potassium  ferrocyanide 
to  a  solution  of  a  ferric  salt.  The 
blue  pigment  formed  is  filtered, 
washed  and  dried.  This  blue  com- 
pound will  produce  a  blue  stock  but 
not  quite  as  good  as  ultramarine.  It 
may  be  used  when  an  acid  resistant 
material  is  needed  and  ultramarine 
cannot  be  used.  On  the  other  hand, 
however,  alkalis  will  decompose  it. 
Prussian  blue  does  not  withstand 
the  effect  of  vulcanization  as  well  as 
ultramarine  blue. 

Thenard's  Blue 

Thenard  's  Blue  is  made  by  heating 
together  in  a  covered  crucible  alumi- 
num and  cobalt  phosphates.  The  blue 
color  which  is  obtained  will  depend 
upon  the  proportion  of  aluminum  and 
cobalt  used :  the  more  cobalt  employed 
the  darker  will  be  the  shade  of  blue. 
This  pigment  is  not  used  to  any  great 
extent. 

In  these  two  chapters,  which,  on 
account  of  the  material  they  contain 
appear  very  choppy,  we  have  tried 
to  give  the  reader  a  little  insight  into 
the  commonest  of  ingredients  used 
in  the  rubber  industry. 


CHAPTER  XIII 
The  Manufacture  and  Use  of  Organic  Accelerators 


In  the  minds  of  some  people  there 
seems  to  exist  a  misunderstanding  in 
regard  to  the  terms  "  accelerators  " 
and  "  catalysts."  Therefore  it  does 
not  seem  out  of  place  here  to  point 
out  the  true  meaning  and  correct  use 
of  the  two  terms. 

Brezelius  knew  that  hydrogen 
peroxide,  if  allowed  to  stand  by  itself, 
decomposed  very  slowly  into  water 
and  oxygen.  He  also  knew,  however, 
that  if  to  this  hydrogen  peroxide  was 
added  a  small  amount  of  finely 
divided  platinum,  a  rapid  decomposi- 
tion of  the  peroxide  took  place  and  a 
great  volume  of  oxygen  was  liberated. 

He  went  further  and  found  out 
that  the  platinum  was  not  changed  in 
itself  in  any  way  and  that  a  small 
amount  of  platinum  was  capable  of 
transforming  an  indefinite  amount  of 
hydrogen  peroxide  into  water  and 
oxygen.  The  t\vo  elements,  hydro- 
gen and  oxygen,  will  remain  mixed 
together  at  ordinary  temperature  al- 
most indefinitely  without  any  chemi- 
cal union,  but  if  a  little  platinum 
sponge  is  introduced  into  the  mix- 
ture, the  union  immediately  takes 
place,  yet  the  platinum  remains  un- 
changed. 

Sulphur  dioxide  does  not  combine 
with  oxygen  under  ordinary  condi- 
tions but  in  the  presence  of  platinized 
asbestos,  the  two  react  and  form  the 
anhydride  of  sulphuric  acid,  thus  the 
production  of  sulphuric  acid  today 
by  the  ' '  Contact  Process. ' ' 

By  these  three  examples  it  will  be 
seen  that  certain  reactions  are  made 
to  take  place  under  certain  condi- 
tions, by  the  addition  of  what  might 
be  regarded  as  a  foreign  substance. 
This  foreign  substance  is  necessary  to 
change  the  speed  of  the  reaction  and 


is  not  changed  in  the  least  by  it  as 
far  as  we  know.  Such  substances 
Brezelius  called  "  catalysts."  their 
action  he  called  "  catalytic  "  and  the 
phenomenon  "  catalysis."  Catalysts 
will  not  incite  reactions  to  take  place 
which  would  not  take  place  at  all  but 
they  do  wonderfully  affect  the  speed 
of  these  reactions. 

Action  of  Catalysts 

It  has  been  suggested  that  these 
catalysts,  in  effecting  their  work, 
form  intermediate  products  which 
are  very  unstable  and  break  down 
giving  the  products  of  the  reaction 
and  the  renewed  catalyst.  Such  in- 
termediate products  have  been  proved 
to  exist  and  to  these  has  been  given 
the  name  "  pseudo-catalytic  phe- 
nomena." Ostwald  however  pro- 
poses the  idea  that  they  act  like  a 
lubricating  oil  in  a  rotating  wheel. 
It  turns  very  slowly  and  with  great 
difficulty  when  oil  is  lacking  but 
when  it  is  added,  the  wheel  turns 
freely  yet  the  oil  has  no  part  in  the 
movement.  Here  will  be  seen  the 
analogy  to  catalytic  action. 

Euler  has  advanced  the  hypoth- 
esis that  the  velocity  of  a  reaction  de- 
pends upon  the  free  ion  concentration 
and  that  catalysts  have  the  power  of 
modifying  this  concentration,  for  we 
have,  beside  these  catalysts  which  in- 
crease the  speed  of  a  reaction  and 
are  called  "  positive  catalysts," 
those  which  retard  a  chemical  change 
and  are  called  "  negative  catalysts." 
Here  we  have  set  forth  the  time  con- 
ception of  catalizers,  namely  sub- 
stances which  may  hasten  or  retard 
a  chemical  change  and  yet  are  not 
themselves  affected  in  any  way. 

The  term  accelerators  has  quite  a 
different  meaning  and  application 


85 


86 


RUBBER   MANUFACTURE 


from  a  chemical  point  of  view.  In 
the  first  place,  they  only  increase  the 
velocity  of  the  chemical  changes  and 
secondly  they  may  or  may  not  be 
affected  chemically  themselves. 

In  the  rubber  industry,  therefore, 
we  should  refer  only  to  accelerators, 
for  in  the  vast  majority  of  cases,  the 
substance  which  is  added  to  increase 
the  speed  of  vulcanization  is  in  itself 
changed  also. 

Accelerators 

Only  recently  did  it  occur  to  the 
rubber  chemists  that  it  was  possible 
to  cut  down  the  length  of  time  of 
vulcanization,  without  increasing  the 
steam  pressure,  by  introducing  into 
the  rubber  very  small  amounts  of  or- 
ganic substances  which  would  act  as 
accelerators.  Once  tried  and  the  re- 
sults observed,  the  commercial  im- 
portance of  the  practice  was  immedi- 
ately grasped. 

The  introduction  of  these  sub- 
stances was  suggested  from  the  fact 
that  synthetic  rubber,  or  caoutchouc 
was  very  difficult  to  vulcanize,  as  is 
also  acetone  extracted  rubber.  This 
led  to  the  study  of  ways  to  vulcanize 
the  synthetic  product  and  to  the 
study  of  the  acetone  extract  from 
Para  with  the  result  that  nitrog- 
enous bodies  were  found  in  the  ex- 
tract and  the  introduction  of  these 
into  caoutchouc  shortened  its  time  of 
vulcanization. 

The  work  of  research  laboratories 
was  directed  toward  the  producing 
and  perfecting  of  substances  and 
learning  also  how  they  might  be  used. 
It  is  in  the  midst  of  this  kind  of  work 
that  wre  find  ourselves  today.  In  fact 
we  do  not  know  very  much  about  this 
new  line  as  yet  and  we  must  still  be 
very  modest  in  our  claims.  Many 
organic  substances  have  been  experi- 
mented with  in  this  connection  and 
new  ones  are  being  recommended  and 
placed  on  the  market  every  day. 
Some  of  them  appear  under  their 
true  chemical  title  while  others  are 
disguised  under  trade  names.  Re- 
cently this  laboratory  received  one 
from  a  commercial  house  with  the  re- 
quest that  some  experimental  work  be 
done  with  it  and  with  the  statement 
that  they  had  not  named  it  as  yet. 


Several  theories  have  been  ad- 
vanced as  to  the  part  which  these 
substances  really  play  in  hastening 
the  cure  of  rubber  articles,  but  we 
shall  leave  those  to  a  future  chapter. 

In  this  section  we  shall  consider 
only  a  few  accelerators  and  those  are 
the  ones  in  commonest  use.  It  is 
held  today  that  only  nitrogen  com- 
pounds will  act  as  accelerators,  and 
only  those  capable  of  being  easily 
handled,  easily  incorporated  into  the 
stock,  and  possessing  great  enough 
stability  not  to  produce  "  blowing  " 
during  vulcanization,  may  be  used. 
One  of  the  first  substances  of  this 
kind  to  be  used  was  aniline. 

Aniline  is  made  from  nitro-benzene, 
which  is  made  from  benzene.  This  is 
effected  in  large  cast  iron  vessels 
where  a  mixture  of  nitric  and  sul- 
phuric acids  is  gradually  poured  into 
benzene.  It  is  constantly  stirred  and 
the  temperature  maintained  at  25 
deg.  During  the  latter  part  of  the 
reaction  the  temperature  is  raised  to 
from  70  deg.  to  90  deg.  The  mix- 
ture is  then  forced  into  a  conical 
tank  when  the  acid  mixture  settles  to 
the  bottom  and  is  drawn  off.  The 
nitrobenzene  is  washed  several  times 
with  water  and  then  distilled  in  a  cur- 
rent of  steam.  The  equation  for  its 
production  may  be  indicated  thus. 
CH 

0 

il 
-f  H  —  0  —  N  — ; > 


0 


110II 


The  nitrobenzene  is  then  placed  in 
a  cast  iron  cylinder  provided  with  a 
stirrer,  a  reflex  condenser  and  an 
opening  for  introducing  iron  filings. 
Some  water  is  placed  in  the  cylinder, 
some  iron  turnings  and  hydrochloric 
acid.  These  are  kept  stirred  while 
nitrobenzene  is  added.  The  reaction 


THE  MANUFACTURE  AND  USE  OF  ORGANIC  ACCELERATORS 


87 


may  be  started  by  a  jet  of  steam. 
Afterward,  however,  it  will  maintain 
its  own  temperature  for  operation,  in 
fact  one  must  guard  against  its  get- 
ting too  hot.  At  the  end  of  the 
operation  we  have  aniline,  aniline 
hydrochloride,  ferric  oxide,  some  un- 
altered nitrobenzene  and  other  im- 
purities. The  main  reaction  which 
has  taken  place  may  be  represented 
thus. 


4-  6HC1  +  3Fe 


CNH, 


-f  2HOH  +  3FeCl2 


But  in  actual  working  conditions  it 
requires  only  about  one-fourth  of  the 
theoretical  amount  of  hydrochloric 
acid,  thus  showing  that  after  a  cer- 
tain concentration  is  reached,  the  re- 
duction is  then  effected  by  the  action 
of  iron  on  water  in  the  presence  of 
ferrous  chloride  in  the  following  man- 
ner : 

CNO, 


+  2Fe  +  4HOH 


CNH, 


+2Fe(OH); 


After  the  reduction  is  complete, 
thick  milk  of  lime  is  added  until  a 
distinct  alkaline  reaction  is  obtained 
when  the  mass  is  distilled  with  steam. 
The  distillate  will  separate  into  two 
layers,  the  aniline  being  in  the  lower 
portion.  This  is  often  purified  by 
redistillation.  Aniline  has  a  boiling 


point  of  183  deg.  to  184  deg.  and  a 
specific  gravity  of  1.024  at  16  deg.  C. 
It  is  colorless  when  pure,  but  becomes 
brown  in  the  air  at  a  rate  depending 
upon  the  amount  of  impurities 
present. 

This  aniline  oil  has  been  used  as  an 
accelerator  by  simply  pouring  the  oil 
into  the  compound  when  it  has  broken 
down  on  the  hot  mills.  The  vapors 
which  came  off  from  the  mill  were 
very  injurious  to  the  workmen,  giving 
them  aniline  poisoning.  The  aniline 
acts  upon  the  nervous  system  and 
even  a  small  amount  will  turn  the 
lips  bluish  and  produce  the  effect  of 
drunkenness,  the  patient  becoming 
very  pale  and  being  affected  with  loss 
of  appetite.  The  use  of  alcoholic 
liquors  seems  to  be  very  harmful  to 
one  suffering  from  aniline  poisoning. 

Factories  in  which  aniline  was  be- 
ing used  went  to  great  expense  to 
install  ventilating  systems  with  large 
hoods  over  the  mills.  It  hastens  the 
cure  of  rubber  articles;  makes  vul- 
canization possible  in  a  shorter  time 
and  also  with  the  addition  of  less 
sulphur,  which,  of  course,  cute  down 
the  possibility  of  blooming.  Aniline 
is  a  solvent  for  sulphur  and  that  may 
have  its  influence  upon  shortening  the 
time  of  cure  as  we  know  reactions 
take  place  more  rapidly  in  solutions 
or  homogeneous  systems  than  in 
heterogeneous  ones.  The  use  of  ani- 
line alone  has  been  practically  aban- 
doned today  in  favor  of  those  less 
harmful  to  the  workmen  and  those 
existing  in  a  form  more  easily  han- 
dled. It  serves,  however,  as  a  base 
for  the  production  of  some  acceler- 
ators widely  used  at  present. 

One  of  the  first  ones  to  be  used  and 
one  that  is  still  widely  used  is  the 
product  which  is  formed  when  aniline 
and  carbon  bisulphide  are  brought 
together.  The  principal  product 
which  is  formed  is  diphenylthiourea 
or  thiocarbanilide.  The  reaction  which 
takes  place  may  be  expressed  thus  : 

S  NHC6H5 

||       NH,C6H, 

C  =  S      +  H2S 

S  NHC0H5 

To  produce  this  substance  in  the  pure 


NH2CCH5 


88 


RUBBER   MANUFACTURE 


form.  Gatterman  gives  the  following 
procedure : 

"  A  mixture  of  40  grams  of  ani- 
line, 50  grams  of  carbon  bisulphide, 
and  10  grams  of  finely  pulverized 
potassium  hydroxide  is  gently  boiled 
for  three  hours  in  a  water  bath  in  a 
flask  provided  with  a  reflux  con- 
denser. The  excess  of  carbon  bisul- 
phide and  alcohol  is  then  distilled  off, 
the  residue  treated  with  water,  the 
crystals  separating  out  are  filtered  off 
and  washed  first  with  water,  then 
with  dilute  hydrochloric  acid,  and 
finally  with  water.  To  obtain  a  high 
degree  of  purity,  it  is  crystallized 
from  alcohol." 

To  produce  the  commercial  prod- 
uct, all  that  is  necessary  is  to  place 
the  mixture  of  aniline  and  carbon 
disulphide  in  large  crocks  or  kettles 
in  a  warm  place,  where  the  escaping 
hydrogen  sulphide  will  be  carried 
away.  The  reaction  will  require  per- 
haps thirty-six  hours  but  it  may  be 
accelerated  by  the  addition  of  sodium 
polysulphide.  The  yield  is  quantita- 
tive and  there  results  a  yellow,  hard, 
crystalline  mass.  This  is  removed, 
pulverized,  dried  and  is  ready  for  use. 

It  should  have  a  melting  point  of 
154  deg.  C.  As  an  accelerator  it  is 
used  in  amounts  from  one-half  to  two 
per  cent  of  the  mixture. 

In  using  this  material,  great  care 
should  be  taken  to  reduce  it  to  a  fine 
powder.  In  grinding  it  tends  to  flake 
up,  making  it  rather  difficult  to  ob- 
tain the  fine  powder.  If  it  is  not  re- 
duced to  a  fine  state  of  division,  it 
will  not  be  incorporated  evenly  in  the 
rubber  and  will  produce  hard  kernels 
of  overcured  rubber  through  the 
product. 

This  substance  shows  its  greatest 
effect  in  accelerating  cure  at  the  be- 
ginning of  the  process  and  thus  great 
care  must  be  used  in  milling  it  for  if 
the  rolls  get  too  warm,  vulcanization 
will  begin.  This  same'  substance, 
thiocarbanilide,  may  be  obtained  in 
the  market  under  the  name  of  "  Ex- 
cellerex. ' ' 

Tetramethylenediamine  is  an  ac- 
celerator which  gives  fair  results  in 
the  final  product,  yet  is  not  to  be  re- 
garded as  rapid  in  its  actions  as  some 
of  the  others. 


This  substance  is  produced  dur- 
ing the  putrefaction  of  animal  mat- 
ter and  is  called  putrescene.  In 
this  connection  we  might  call  atten- 
tion to  the  results  of  Eaton  and 
Grantham's  experiments  in  the  rapid 
curing  of  rubber.  It  will  be  remem- 
bered that  they  obtained  a  fast  cur- 
ing rubber  when  they  coagulated  by 
means  which  would  allow  of  the 
putrefaction  of  some  nitrogenous 
matter,  and  the  thought  arises  that 
this  accelerating  action  may  be  due 
to  the  formation  of  tetramethylene- 
diamine. 

It  may  be  produced  on  the  com- 
mercial scale  by  first  treating  ethyl- 
alcohol  with  sulphuric  acid,  when  the 
following  reaction  takes  place : 
C2H6OH  +  H2S04 — »-  C2HDS04H  +  HOH 
with  the  formation  of  ethyl  sulphuric 
acid.      This    substance    then    decom- 
poses and  yields  ethylene  thus : 
C2H5S04H >  C2H4  +  H2S04 

If  the  ethylene  gas  is  then  passed 
into  bromine,  the  ethylene  bromide 
is  immediately  formed. 

C  =  H2      Br          Br  —  C  =  H2 

C-H,      Br          Br  —  C  =  H2 

Upon  treating  the  ethylene  bromide 
with  potassium  cyanide,  the     nitrile 
will  be  formed. 
Br  KCN         CN 


KCN 


Br 


C  =  II, 


CN 


-f  2KBr 


This  nitrile  upon  reduction  with 
sodium  in  a  hot  alcoholic  solution 
yields  the  tetramethylenediamine. 

CN 

C  =  H2 
C  =  H2 

CN 

H2N  CH2-CH2  CH2-CH2-NH2 

The  substance  is  crystalline  in  nature 
and  easily  incorporated  into  the  rub- 
ber. 

Another  product  related  to  the  one 
above  is  hexamethylenetetramine. 


THE  MANUFACTURE  AND  USE  OF  ORGANIC  ACCELERATORS 


89 


It  is  used  in  small  quantities  to  di- 
sulphur  musts  and  wines.  Here  it  is 
called  urotoropine.  However,  in  this 
use  it  is  in  connection  with  sulphur 
as  is  also  its  use  in  the  vulcanization 
of  rubber.  This  substance  is  a  deriva- 
tive of  formaldehyde  and  results 
when  formaldehyde  is  treated  with 
ammonia.  Its  reaction  is  shown  in 
the  following : 
CHCOH+4NH,  — y  (CH2)0N,+6HOH 

F.  Hermann  has  given  the  follow- 
ing method  for  the  production  of  this 
substance.  To  the  formalin  in  a  closed 
receptacle,  he  added  ammonium  chlo- 
ride in  quantity  sufficient  to  liberate 
enough  ammonia  to  effect  the  above 
reaction  with  the  amount  of  forma- 
lin taken,  then  enough  caustic  soda  to 
free  this  ammonia  from  the  ammo- 
nium salt.  As  rapidly  as  the  am- 
monia is  liberated,  it  will  react  with 
the  formalin  and  produce  hexa- 
methylenetetramine.  This  substance 
finds  a  wide  use  today  as  an  accel- 
erator of  vulcanization. 

Paraphenylenediamine  also  is  an 
accelerator  quite  largely  employed  in 
the  rubber  industry  today  and  yet 
it  is  a  very  poisonous  substance.  Great 
care  should  be  taken  where  it  is  used 
to  guard  the  welfare  of  the  work- 
men. It  is  regarded  as  one  of  the 
rapid  accelerators.  It  may  be  made 
in  several  ways.  First  by  the  reduc- 
tion of  aminoazobenzene  dissolved  in 
aniline,  with  hydrogen  sulphide  or  tin 
and  hydrochloric  acid.  Second,  by 
heating  paradichlorobenzene  or  para- 
chloraniline  with  ammonia  in  the 
presence  of  a  copper  salt.  (Ger.  Pat. 
204408). 

Beginning  with  aniline  in  the  first 
method,  the  following  steps  are  neces- 
sary according  to  Holleman. 

Aniline  treated  with  sodium  nitrite 
in  the  presence  of  hydrochloric  acid 
gives  diazobenzenechloride,  thus: 
C0H5NH,  +  XaN<X  +  2HC1— > 
C6H5N  -NCI  +  2HOH  +  NaCl 

When  this  is  treated  with  aniline  the 
diazoaminobenzenechloride  is  pro- 
duced. 


One  of  the  most  characteristic  re- 
actions of  these  diazoaminobenzenes 
is  their  easy  conversion  into  isomers, 
or  the  aminoazo  compounds.  This  is 
best  carried  out  by  adding  aniline 
hydrochloride  to  a  solution  of  diazo- 
aminobenzene  in  aniline  and  warming 
the  mixture  on  a  water  bath. 

C6H5N-N-NHC6H5 > 

CGH5N-N-C6H4NH2 

Here  the  amino  group  is  in  the  para- 
position  to  the  azo  group.  When  this 
compound  is  reduced  there  results 
aniline  and  paraphenylenediamine. 

C6H5N     NC0H4NH, 
H2   H2 

XH2 

C 


CNH, 

The  second  method  is  very  simple  as 
indicated  above. 


:  Cl    H  .*  NH, 


NH. 


or 


H: 


ci  H  •  NH, 


C6H6N-N 


NHCH 


Under  the  trade  name  of  "  Accele- 
rene,"  we  find  the  substance  para- 
nitrosodimethylaniline.  It  may  be 
made  by  heating  aniline  hydro- 
chloride  with  methyl  alcohol. 

NH,HC1 


+  2CH3OH 


90 


RUBBER   MANUFACTURE 


+  2HOH  +  HC1 


The  hydrogen  in  the  para-position  of 
these  dialkylamines  is  readily  re- 
placed by  different  groups.  Thus  the 
action  of  nitrous  acid  yields  para- 
nitrosodimethylaniline.  This  sub- 
stance possesses  a  greenish  color  and 
should  have  a  melting  point  of  about 
85  deg.  C. 

Piperidine  and  some  of  its  derivi- 
tives  have  been  used,  but,  owing  to  the 
poisonous  nature  of  these  substances 
and  their  odor,  they  are  not  used  to 
any  great  extent. 

Piperidine  is  made  by  reducing 
pyridine  with  sodium  and  alcohol. 


NH 


It  is  a  liquid  possessing  an  odor  of 
pepper.  It  acts  directly  as  an  ac- 
celerator, however,  upon  vulcaniza- 
tion. 

Quinoline  and  its  derivatives  are 
used  in  a  satisfactory  manner  to  a 
limited  extent.  Quinoline  being  the 
base  of  these,  we  shall  outline  only 
methods  for  the  production  of  that 
substance.  It  is  found  in  coal-tar  and 
bone  oil  but  is  difficult  to  obtain  from 
these  sources. 

Konigs  first  synthesized  it  by  pass- 
ing allylaniline  vapor  over  red  hot 
lead  oxide,  when  the  following  reac- 
tion took  place. 


+  20 


H 


Skraup's  synthesis  for  quinoline  as 
outlined  by  Perkin  and  Kipping  is 
as  follows:  "  Concentrated  sulphuric 
acid  100  parts  is  gradually  added  to 
a  mixture  of  aniline,  38  parts,  and 
nitrobenzene,  24  parts,  and  glycerine, 
120  parts,  and  the  mixture  is  then 
very  cautiously  heated  in  a  large 
flask  (with  reflux  apparatus)  on  a 
sand  bath ;  after  the  very  violent  re- 
action which  soon  sets  in  has  subsided, 
the  liquid  is  kept  boiling  for  about 
four  hours.  It  is  then  cooled,  diluted 
with  water,  and  the  unchanged  nitro- 
benzene separated  by  distillation  with 
steam;  soda  is  then  added  in  excess 
to  liberate  the  quinoline  and  the  un- 
changed aniline  from  their  sulphates 
and  the  mixture  is  again  steam  dis- 
tilled. As  these  two  bases  cannot  well 
be  separated  by  fractional  distilla- 
tion, the  whole  of  the  aqueous  distil- 
late is  acidified  with  sulphuric  acid 
and  sodium  nitrite  added  until 
nitrous  acid  is  present  after  shaking 
well.  After  heating,  to  convert  the 
diazo  salt  into  phenol,  the  solution  is 
rendered  alkaline  with  soda  and  again 
submitted  to  distillation  with  steam. 
The  quinoline  in  the  receiver  is  finally 
separated  with  the  aid  of  a  funnel 
and  purified  by  fractional  distilla- 
tion." It  is  a  liquid  with  a  peculiar 
odor. 


+  CHOH  +  0- 


+  4HOH 


II 


NH 


This,  being  a  liquid,  is  not  easily 
handled  so  it  is  converted  into  its 
sulphate  and  used  most  frequently 


THE  MANUFACTURE  AND  USE  OF  ORGANIC  ACCELERATORS 


91 


thus.  It  is  made  by  dissolving  the 
quinoline  in  dilute  sulphuric  acid, 
when  the  sulphate  (C9HTN)2H2S04 
crystallizes  out. 

In  addition  to  the  ones  mentioned 
above,  many  more  have  been  tried ;  in 
fact,  derivatives  of  all  possible  nitro- 
gen compounds  have  been  experi- 
mented with.  Derivatives  of  the  pro- 
teins of  urea  and  ammonium  com- 
pounds have  all  been  recommended 
for  this  use. 

Aldehyde  ammonia,  which  is  pro- 
duced by  passing  dry  ammonia  gas 
into  a  solution  of  formalin,  is  a  very 


good  accelerator.  It  tends,  however, 
to  make  the  finished  product  harsh 
rather  than  of  a  velvety  appearance. 

Many  substances  which  will  ac- 
celerate must  be  discarded,  for  accel- 
eration of  cure  alone  is  not  a  suf- 
ficient test  for  them.  In  addition  to 
shortening  the  time  for  curing,  they 
must  also  increase  the  physical  prop- 
erties of  the  rubber  and  thus  reduce 
the  deterioration  of  the  finished  prod- 
ucts. So  research  along  this  line  will 
continue  even  though  at  present  we 
seem  to  be  settling  down  to  a  few 
common  accelerators. 


CHAPTER  XIV 
The  Manufacture  and  Use  of  Rubber  Substitutes 


In  this  chapter,  we  shall  consider 
those  materials  which  are  used  in  the 
rubber  industry  along  with  rubber 
compounding,  and  the  ones  we  shall 
mention  contain  no  rubber  in  them- 
selves, yet  by  their  use,  the  actual 
amount  of  true  rubber  used  may  be 
reduced.  The  introduction  of  these 
materials  must  be  done  in  such  a  way 
as  not  to  be  injurious  to  the  final 
product,  and  likewise  the  substances 
themselves  must  not  impair  the  phys- 
ical properties  of  the  articles. 

The  justification  of  the  use  of 
these  materials  in  the  beginning  was 
especially  to  cut  down  the  cost  of 
the  rubber  goods  by  introducing 
some  materials  possessing  properties 
like  rubber  yet  which  could  be  pro- 
duced at  a  much  smaller  cost. 

Such  materials  were  found  possible 
of  production  from  many  drying  and 
even  non-drying  oils.  It  has  been 
observed  and  known  for  many  years 
mat  certain  vegetable  oils  when  ex- 
posed in  a  thin  film  to  the  air,  or 
when  in  other  words,  were  allowed  to 
dry,  formed  a  skin  which  possessed  a 
few  properties  of  rubber,  such  as 
toughtness  and  elasticity  to  a  certain 
degree.  What  has  really  taken  place 
is  that  the  oil  has  been  slowly  taking 
up  oxygen  and  has  been  converted 
into  this  semi-rubber  like  condition. 

As  early  as  1846,  Sacc  produced  a 
rubber  like  material  by  actually  oxi- 
dizing linseed  oil  rapidly  by  the  use 
of  nitric  acid.  If  linseed  oil  is  heated 
in  contact  with  air  until  it  has  oxi- 
dized to  the  state  of  a  semi-solid  mass, 
then  nitric  acid  is  added  and  the 
heating  continued,  it  will  finally 
arrive  at  such  a  state  that  when 
cooled  in  the  air,  a  solid  material  re- 
sults. This  substance  resembles  rub- 
ber in  appearance,  is  more  or  less 


elastic,  softens  in  hot  water,  and  is 
soluble  in  turpentine,  carbon  d'sul- 
phide,  and  alkalies.  When  an  alka- 
line solution  of  this  product  is 
treated  with  hydrochloric  acid,  it  is 
precipitated  unchanged.  This  prop- 
erty of  oil  of  being  changed  by  a 
process  of  oxidation  in  this  manner 
is  characteristic  of  drying  oils  in  con- 
trast to  non-drying  oils,  which  upon 
exposure  to  the  air  become  rancid. 
This  oxidized  oil  is  known  as  "  Oil 
Rubber,"  and  because  it  is  of  com- 
mercial importance  a  more  rapid 
method  for  its  production  was  nec- 
essary. By  the  process  mentioned, 
above,  the  oxidation  takes  place  only 
at  the  surface  of  the  oil,  or  where  it 
comes  in  contact  with  the  oxygen  of 
the  air. 

To  expose  a  greater  surface  of  the 
oil  to  the  oxidizing  agent,  a  process 
has  been  patented  whereby  the  hot, 
finely  divided  oil  comes  in  contact 
with  the  air.  This  shortens  the  time 
of  blowing  the  oil  very  materially. 
The  final  oxidation,  however,  is 
effected  with  nitric  acid.  The  concen- 
trated nitric  acid  is  diluted  with  twice 
its  volume  of  water  and  this  and  the 
thick  blown  oil  are  boiled  together. 
The  oil  becomes  thicker  and  thicker, 
but  boiling  is  continued  until  a  sam- 
ple, when  cold,  will  scarcely  take  the 
impress  of  a  finger-nail.  When  this 
stage  is  reached,  it  is  removed  from 
the  acid  and  is  washed  with  boiling 
water  until  it  is  free  from  acid  as 
determined  by  actual  test.  The  oil 
rubber  may  now  be  formed  into  any 
desired  shape  and  is  ready  for  the 
market.  It  is  used  as  an  insulating 
material  for  electric  wires. 

Because  of  this  property  of  oils  to 
form  addition  products  with  oxygen, 
and  due  to  the  chemical  analogy 


92 


THE  MANUFACTURE  AND  USE  OF  RUBBER  SUBSTITUTES 


93 


which  exists  between  oxygen  and  sul- 
phur, and  the  fact  that  sulphur  is 
used  in  the  vulcanization  of  rubber, 
it  occurred  to  someone  that  it  might 
be  possible  to  cause  the  oils  to  form 
addition  products  with  sulphur 
similar  to  those  with  oxygen.  In 
other  words  it  seemed  possible  to  pro- 
duce a  "  vulcanized  oil  "  with  prop- 
erties more  nearly  like  those  of  rub- 
ber than  oil  rubber  possessed. 

Thus  it  was  found  that  by  heating 
certain  oils  with  sulphur,  there  re- 
sulted a  substance  possessing  some  de- 
gree of  elasticity.  This  method  of 
heating  an  oil  with  sulphur  produces 
a  dark  colored  product  and  this  is  re- 
ferred to  as  "  Brown  or  Black  Substi- 
tute "  or  "  Brown  Factis."  Its  pro- 
duction resembles  the  "  hot  cure  " 
process  in  the  vulcanization  of  rubber 
itself.  The  oils  most  frequently  used 
for  this  purpose  are  linseed,  maize, 
cotton  seed,  and  rape  oil. 

Many  formulas  and  methods  of 
procedure  to  produce  Brown  Substi- 
tute have  been  given  from  time  to 
time,  but  we  shall  outline  but  three. 

First,  from  linseed  oil.  If  this  oil 
is  heated  to  100  deg.  C.  and  then  from 
5  to  10  per  cent  of  sulphur  is  added 
and  the  temperature  gradually 
raised  to  130  deg.  C.,  then  allowed  to 
cool  back  to  100  deg.  C.  and  held 
at  that  temperature  for  some  time, 
the  vulcanizing  will  be  complete. 
When  the  reaction  is  finished,  the 
product  is  cooled  on  a  smooth  cold 
surface. 

Second,  if  8  gal.  of  corn  oil  are 
placed  in  a  large  boiler  and  rapidly 
brought  to  a  temperature  of  390  deg. 
F.,  during  the  heating  a  frothy  curd 
will  form  over  the  surface  of  the  oil 
which  must  be  removed.  During 
this  heating,  a  current  of  hot  air  is 
blown  through  the  oil  which  causes 
it  to  become  more  or  less  viscous.  At 
this  point,  0.20  Ib.  of  sulphur,  which 
has  been  previously  melted,  are 
added  in  the  molten  state.  A  vigor- 
ous reaction  immediately  begins  and 
the  whole  mass  froths  up  and  is  then 
poured  into  cooling  boxes  where  it  is 
stirred  and  allowed  to  cool.  Black 
substitute  then  results. 

The  sulphur  used  here  must  be 
free  from  sulphurous  acid  and  this 


fact  must  be  determined  by  analysis. 
This  black  substitute  may  be  soft- 
ened by  heat  and  cast  into  blocks  and 
we  find  it  in  the  industry  largely  in 
this  form. 

Another  process  for  making  Brown 
substitute  from  corn  oil  has  been  pat- 
ented by  William  K.  Leonard.  This 
patent  calls  for  76  per  cent  of  corn 
oil,  21  per  cent  of  sulphur  and  3  per 
cent  of  paraffin.  The  oil  is  placed  in 
a  kettle  where  it  may  be  heated  and 
when  a  temperature  a  little  below  300 
deg.  F.  is  reached,  the  sulphur  and 
paraffin  are  added.  The  temperature 
is  still  raised  and  at  about  310  deg. 
F.  the  reaction  begins  and  the  source 
of  heat  is  removed.  The  reaction 
will  continue  of  its  own  accord,  and  in 
fact  it  being  an  exothermal  reaction, 
the  temperature  will  continue  to  rise 
often  reaching  340  deg.  F.  during  the 
process.  The  product  is  allowed  to 
cool  and  is  then  ready  to  be  incor- 
porated into  rubber  compounds.  (U. 
S.  Pat.  615,  863.) 

In  1846,  Alexander  Parkes  mixed 
some  linseed  oil  with  from  20  to  40 
per  cent  of  sulphur  monochloride 
and  found  that  vulcanization  would 
take  place  and  a  light-colored  product 
result,  what  we  call  today  "  White 
Substitute  "  or  "  White  Factis." 
This  process  is  analogous  to  the  ' '  cold 
cure  "  which  is  used  with  rubber. 
It  was  found  out  later  that  if  the 
oil  was  first  dissolved  in  carbontetra 
chloride  the  reaction  would  take 
place  in  a  great  deal  better  manner, 
thus  more  nearly  resembling  the  cold 
cure  vulcanization. 

Only  small  quantities  of  oil  are 
treated  at  a  time  as  the  exothermal 
reaction  causes  such  a  rise  in  tem- 
perature that  there  results  a  big  loss 
of  the  sulphur  monochloride  and  the 
oil  itself  will  carbonize.  The  mono- 
chloride  used  must  be  free  from  the 
dichloride  of  sulphur.  This  is  very 
objectionable  as  it  causes  too  violent 
a  reaction  with  the  result  that  the 
oil  carbonizes  and  rlie  product  is 
burnt. 

The  amount  of  sulphur  taken  up  by 
the  oil  varies  from  5  to  15  per  cent. 
The  amount,  however,  will  depend 
upon  the  degree  of  oxidation  of  the  oil 
before  the  monochloride  is  added,  that 


94 


RUBBER   MANUFACTURE 


is,  partially  oxidized  oils,  or  blown 
oils,  will  not  take  up  as  much  sul- 
phur. This  same  fact  is  true  in  re- 
gard to  the  making  of  Brown  Factis, 
and  that  is  the  reason  that  the  oils  are 
first  heated. 

Henriques  found  that  raw  linseed 
oil  requires  at  least  thirty  parts  of 
sulphur  monochloride  to  solidify 
when  fresh  while  it  requires  only 
fifteen  to  eighteen  parts  when  it  has 
been  heated  for  some  hours  at  200  deg. 
C.  in  contact  with  the  air.  He  also 
observed  that  if  the  temperature  is 
raised  from  250  deg.  to  300  deg.,  then 

10  per  cent  of  sulphur  monochloride 
will  suffice.     All  drying  oils  seem  to 
behave  in  this  same  manner. 

The  same  oils  which  are  used  for 
the  production  of  Brown  Factis  may 
be  employed  for  the  production  of 
the  White.  The  raw  oil  is  placed  in 
shallow  pans,  which  are  constructed 
in  such  a  way  that  air  may  be  blown 
up  through  the  heated  oil  in  them. 
The  oil  is  first  heated  to  a  tempera- 
ture of  392  deg.  F.  to  464  deg.  F.  and 
the  white  scum  which  forms  is  re- 
moved ;  then  air  is  blown  up  through 
the  oil  and  the  temperature  raised  to 
572  deg.  F.  This  partially  oxidized 

011  is  now  run  into  large  storing  tanks 
or  reservoirs  where  it  is  allowed  to 
cool   to  ordinary  temperature.      The 
reason    for    this    treatment,    as    was 
pointed  out  above,  is  to  save  sulphur 
monochloride,    less    of    which    is    re- 
quired with  these  oxidized  oils. 

A  weighed  quantity  of  this  cold 
thick  oil  is  placed  in  a  large  enam- 
eled boiler  and  stirring  is  begun. 
When  the  required  amount  of  sul- 
phur monochloride  is  added,  white 
vapors  will  soon  appear,  indicating 
that  the  reaction  has  begun  and  their 
cessation  will  serve  as  an  indication 
of  the  completion  of  the  reaction. 
The  mixture  of  oil  and  monochloride 
is  maintained  at  a  temperature  of 
131  to  140  deg.  F.  The  factis  is  re- 
moved and  placed  upon  nets,  which 
allow  the  escape  of  the  odor  of  the 
sulphur  monochloride.  The  product 
is  almost  colorless  and  is  not  affected 
by  boiling  with  dilute  acids  and  alka- 
lies in  distinction  from  the  brown 
factis  which  is  soluble  in  alkalies. 


William  K.  Leonard  has  also  pat- 
ented a  process  for  the  production 
of  the  white  substitute.  According 
to  his  patent,  64  per  cent  of  corn 
oil  and  13  per  cent  of  castor  oil  are 
thoroughly  mixed  and  then  21  per 
cent  of  the  entire  mass  of  sulphur 
monochloride,  0.5  per  cent  of  naph- 
tha and  1.5  per  cent  of  oxide  of 
magnesia  are  added.  The  reaction 
immediately  begins  and  the  tempera- 
ture tends  to  rise,  but  when  the  re- 
action is  completed  and  the  whole 
mass  allowed  to  cool,  a  white  spongy 
product  will  result.  (U.  S.  Pat.  615%,- 
864.) 

For  the  production  of  a  white 
factis  from  linseed  oil,  Nicolaus  Reif 
has  patented  a  form  of  apparatus 
for  mixing  the  oil  and  sulphur  mono- 
chloride  under  pressure  in  such  a 
manner  that  the  whole  mass  is  mixed 
by  a  rotary  movement  and  expressed 
from  the  apparatus  by  a  similar 
movement  thus  reducing  the  mixture 
to  a  flake-like  condition.  (U.  S.  Pat. 
1,006,274.) 

Henriques    has    prepared    a    table 
showing    the    production    of    White 
Factis  from  different  oils: 
Linseed  oil  congeals  with  30  parts  sulphur 

monochloride.  but  not  with  25  parts. 
Poppy  oil  congeals  with  35  parts  sulphur 

monochloride,  but  not  with  30  parts. 
Rape  oil  congeals  with  25  parts  sulphur 

monochloride.  but  not  with  20  parts. 
Cotton  seed  oil  congeals  with  45  parts  sul- 
phur   monochloride,    but    not    with    40 

parts. 
Olive  oil  congeals  with  25  parts  sulphur 

monochloride,  but  not  with  20  parts. 
Castor  oil  congeals  with  20  parts  sulphur 

monochloride,  hut  not  with  18  parts. 

It  is  really  remarkable  to  what  ex- 
tent factis  may  be  used  in  rubber 
without  affecting  the  elastic  proper- 
ties of  the  rubber,  in  fact  it  may  be 
added  up  to  a  proportion  of  1:1. 
This  is  due  to  the  mechanical  con- 
sistency of  factis,  which  possesses 
compressile  elasticity,  but  is  desti- 
tute of  tensile  strength.  So  by  its 
addition  we  may  sacrifice  tensile 
strength,  but  not  impair  springi- 
ness. 

The  specific  gravity  of  factis  varies 
between  0.98  and  1.02  and  it  is  the 
only  material  by  which  floating  goods 
may  be  cheapened. 


THE  MANUFACTURE  AND  USE  OF  RUBBER  SUBSTITUTES 


95 


Brown  Factis  often  contains  paraf- 
fin wax  or  heavy  petroleum  frac- 
tions, both  of  which  are  added  to 
the  oil  before  it  is  vulcanized.  Gen- 
erally we  are  safe  in  saying  that  the 
less  there  is  of  unvulcanized  oil  in 
a  substitute  the  better  it  is,  for  the 
free  oils  have  a  tendency  to  shorten 
the  life  of  the  goods.  The  best  "White 
Factises  are  those  which  are  driest 
and  least  coherent  in  the  ground 
state  and  the  combined  per  cents  of 
sulphur  and  chlorine  should  not  ex- 
ceed twenty 

H2C  —  0  —  CO  —  CH,  - 


influence  upon  the  amount  of  sulphur 
to  be  added. 

The  exact  chemistry  of  the  pro- 
duction of  these  substitutes  is  not 
known,  yet  the  possible  steps  may  be 
indicated. 

We  do  know  that  the  oils  which 
are  used  are  glycerides  of  the  fatty 
acids;  therefore  we  may  draw  the 
following  picture  where  two  mole- 
cules of  one  of  these  glycerides  are 
bound  together  by  three  molecules  of 
sulphur  monochloride  S2C12. 

When  this  White  Factis  is  treated 

with  a  boiling  alcoholic  solution  of 

CH  —  CH  —  (CH2)  13  — 


Cl 


S 


Cl         S 

HC  —  0  —  CO  —  Clio  —  CH  —  CH  —  (CH2)  13  —  CH3 
H2C  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)]3  —  CH., 

Cl         S 

Cl         S 

H2C  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)  13  —  CH3 
HC  —  0  —  CO  —  GIL  —  CH  —  CH  —  (CH,)  „  —  CH3 

I  !         I. 

Cl         S 

I 

Cl         S 


H2C  —  0  —  CO  —  CH,  — CH  —  CH  —  (CH2)  13  —  CH 

The  free  sulphur  content  must  be 
known  whenever  a  factis  is  used  in 
compounding  for  this  will  have  its 

3_CH  —  CH  —  y 


N/2  potassium  hydroxide,  it  is 
saponified  and  the  sulphur  atoms 
will  remain  bound  to  the  fatty  acids. 


S         Cl 

I 

S         Cl 
x  —  CH  —  CH  —  y 


2KOH 


S 
S 
x  —  C  = 


+  2KC1  +  2HOH 


96 


RUBBER   MANUFACTURE 


The   Brown    Factis   may   then   be 
represented  in  the  following  manner : 


substance  is  insoluble  in  all  known 
solvents. 


H,C  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)13  —  CH3 

s       s 

HC  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)  13  —  CH:! 
H,C  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)  13  —  CH;i 

S          S 

H2C  — -0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)  13  —  CH3 
HC  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2)  13  —  CH;! 

S          S 


H,C  —  0  —  CO  —  CH2  —  CH  —  CH  —  (CH2; 


CH., 


From  these  formulas  it  will  be 
seen  why  a  partially  oxidized  oil 
will  require  less  sulphur  or  sulphur 
monochloride  for  the  oxygen  will  go 
into  the  substance  in  the  place  of 
these. 

The  substances  which  have  been 
treated  above  are  substitutes  only 
in  the  sense  that  by  their  use,  the 
actual  amount  of  rubber  taken  may 
be  reduced,  but  we  may  mention  a 
few  substances  which  have  been 
made  that  are  substitutes  for  rubber 
itself.  In  other  words,  they  may  be 
made  up  into  articles  in  which  rub- 
ber has  been  used  before.  Such  a 
substance  is  Sulphuretted  Hydro- 
cellulose.  It  was  discovered  by 
Sthamer  and  is  made  by  treating 
finely  ground  hydrocellulose  with 
enough  hydrochloric  acid  of  24  deg. 
Baume  at  ordinary  temperature  to 
form  a  thin  paste  of  the  nature  of  a 
solution.  To  this  sulphur  mono- 
chloride  is  added  and  the  whole  mass 
stirred.  After  some  time  the  fluid 
turns  turbid  and  when  placed  in 
cold  water,  the  sulphuretted  hydro- 
cellulose  settles  to  the  bottom  in  one 
large  mass.  It  is  removed  and 
placed  upon  a  screen  where  it  is  al- 
lowed to  drain  and  the  excess  acid 
thus  recovered,  then  washed  with 
water  until  free  from  the  acid.  This 


When  this  material  is  compounded 
with  rubber  and  then  subjected  to 
vulcanization,  it  will  decompose  and 
give  up  its  sulphur  to  the  rubber 
which  in  turn  is  cured.  It  seems  that 
such  a  substance  might  find  more  ap- 
plication in  the  rubber  industry. 

Several  patents  have  been  taken 
out  by  Julius  Stockhausen  for  the 
making  of  a  substitute  for  india  rub- 
ber. In  one  of  these,  125  grams  of 
gelatin  are  dissolved  in  125  grains 
of  glycerine  and  this  then  mixed 
with  5  to  20  grams  of  sulphur,  20 
grams  of  camphor,  and  15  to  20 
grams  of  colophony.  This  mixture 
is  heated  for  a  long  time  and  there 
is  added  to  it  10  to  20  grams  of  for- 
maldehyde or  3  to  10  grams  of 
sodium  bichromate.  This  produces 
an  elastic  and  plastic  substance. 

He  has  also  patented  the  follow- 
ing formula:  125  grams  of  powdered 
gelatin  or  agar-agar  are  dissolved  in 
125  grams  of  crude  glycerine,  25 
deg.  Baume  at  70  deg.  C.  Then  15 
grams  of  tar  and  25  grams  of  naph- 
thalene are  added  and  finally  20 
grams  of  4  per  cent  formaldehyde  are 
used  for  hardening.  This  substance 
may  then  be  cast  into  molds  of  any 
desired  shape. 

We  might  go  on  and  enumerate 
many,  many  such  substances  which 


THE  MANUFACTURE  AND  USE  OF  RUBBER  SUBSTITUTES 


9T 


have   appeared   from   time   to   time, 
but  it  hardly  seems  advisable. 

Within  the  last  few  years,  the 
practice  of  adding  the  bitumens  and 
pitches  has  become  very  common. 
The  Trinidad  and  Syrian  asphaltum 
has  been  used  for  some  time  in  the 
insulating  of  cables,  but  now  these 
and  bitumen  in  the  form  of  mineral 
rubber  are  being  used  in  compounds 
even  as  high  as  50  per  cent  of  the 
rubber  content.  These  mineral  rub- 
bers are  many  in  number  and  are 
made  from  soft  natural  bitumens  or 
from  blown  petroleum  residues.  In 
the  trade,  we  find  the  substances 
M.R.X.  and  Rubrax  as  examples  of 
these  materials.  The  real  value  of 
any  of  these  must  be  determined  by 
actual  use  and  their  properties  de- 
termined by  mixing  and  vulcanizing. 
A  great  deal  has  been  said  and  writ- 
ten of  late  in  regard  to  the  different 
effects  produced  by  high  and  low 


softening  point  products.  We  do  not 
wish  to  enter  into  that  controversy 
here,  but  it  has  been  claimed  that 
high  softening  point  mineral  rubber 
produces  a  high  tensile  rubber  but 
one  with  low  resiliency,  while  low 
softening  point  material  produces  a 
low  tensile  but  good  resiliency.  Thus 
we  have  an  excuse  for  the  manufac- 
ture of  both  grades. 

Some  resins  of  natural  occur- 
rence are  used  as  rubber  substitutes 
and  we  simply  wish  to  mention 
rosin,  shellac,  copal,  acroides,  san- 
darac,  dammar  which  are  regarded 
as  resins  proper.  Then,  we  find 
growing  in  the  tropical  regions 
plants  which  produce  a  resin  con- 
taining also  a  certain  percent  of  rub- 
ber itself.  These  substances  appear 
under  the  names  of  Jelutong,  Palem- 
bang,  Pontianak  and  Dead  Borneo. 
These  materials  all  find  a  limited  use 
in  the  rubber  industrv. 


CHAPTER  XV 
Theories  of  Vulcanization 


The  term  vulcanization  is  derived 
from  "  Vulcan,"  the  Roman  fire  god, 
its  connection  with  regard  to  rubber 
being  therefore  the  heat  which  causes 
rubber  when  mixed  with  sulphur,  to 
assume  entirely  different  physical 
and  chemical  properties. 

There  are  two  general  methods  of 
vulcanization,  namely,  what  is  known 
as  the  "  cold  cure  "  and  the  "  hot 
cure  vulcanization."  The  former  is 
effected  by  the  use  of  a  sulphur  mono- 
chloride  solution,  which  acts  upon  the 
rubber,  and  as  it  is  a  surface  action, 
it  may  be  employed  only  with  very 
thin  articles.  This  method  is  also 
allowed  to  take  place  by  placing  the 
articles  to  be  vulcanized  in  the  vapors 
of  sulphur  monochloride. 

The  credit  for  this  process  belongs 
to  Parkes,  who,  in  1846,  dipped  thin 
strips  of  caoutchouc,  for  different 
lengths  of  time,  in  to  a  solution  of  100 
parts  of  carbon  disulphide  and  2.5 
parts  of  sulphur  monochloride.  After 
dipping  these  strips,  he  quickly  dried 
them  at  78  deg.  F.  and  then  washed 
them  in  warm  water.  The  process 
has  been  modified  somewhat  since  his 
day  but  the  essential  features  were 
known  to  him. 

The  credit  for  the  "  hot  vulcaniza- 
tion "  should  be  divided  between 
Hancock  and  Goodyear,  who  inde- 
pendently discovered  that  rubber, 
when  heated  in  contact  with  sul- 
phur, changes  its  properties  very  ma- 
terially. 

They  arrived  at  this  conclusion, 
however,  by  slightly  different  means. 
Hancock  in  1843  patented  a  process 
for  vulcanization  whereby  he  sub- 
jected sheets  of  rubber  to  the  action 
of  molten  sulphur  heated  to  a  tem- 
perature of  284  deg.  to  302  deg.  F., 
when  the  rubber  took  up  10  to  15 


per  cent  of  sulphur.  Of  course,  these 
sheets  had  a  great  tendency  to  bloom, 
so  he  washed  them  with  a  solution  of 
soda.  At  the  same  time  Hancock 
was  trying  these  experiments,  Good- 
year was  working  along  the  same 
lines,  only  he  was  mixing  the  sulphur 
into  the  rubber,  until  he  had  a  homo- 
geneous mixture  which  he  subjected 
to  a  high  temperature.  Of  course,  the 
two  results  were  similar,  but  Good- 
year's  method  being,  in  many  ways, 
the  easiest  to  control,  is  the  one  which 
has  survived.  Gerard  found  that  it 
was  possible  to  effect  vulcanization  by 
subjecting  the  rubber  for  three  hours, 
under  a  pressure  of  four  atmospheres 
in  a  solution  of  calcium  pentasulphide, 
to  a  temperature  of  265  deg.  F.  The 
articles  are  then  removed  and  washed 
with  warm  water.  They  are  well 
cured  and  will  possess  a  velvety 
appearance.  The  length  of  time  they 
must  remain  in  such  a  bath,  of  course, 
is  determined  by  the  thickness  of  the 
articles  to  be  vulcanized. 

Victor  Henri  in  1909-10,  first  ex- 
posed rubber  to  the  action  of  ultra- 
violet rays  and  found  that  it  under- 
went a  kind  of  oxidation.  Later  it 
was  found  that,  if  a  solution  of  rub- 
ber containing  sulphur  wTas  subjected 
to  the  ultra-violet  rays,  the  whole  mass 
became  thick  and  of  a  gelatinous 
nature,  and  by  test  showed  combined 
sulphur.  These  vulcanized  solutions 
may  be  used  for  rubberized  cloth, 
used  as  cements,  for  rubberizing 
leather,  or  used  in  repair  work  of  all 
kinds. 

The  French  have  called  this  proc- 
ess "  Cuisson  "  and  the  Germans 
"  burning  "  but  today  "  vulcaniza- 
tion ' '  seems  to  be  the  accepted  term. 

Inasmuch  as  the  hot  vulcanization 
process  is  dependent  upon  the  tem- 


98 


THEORIES  OF  VULCANIZATION 


99 


100 


RUBBER   MANUFACTURE 


perature  to  which  the  rubber  is  sub- 
jected, as  will  be  pointed  out  later,  it 
is  very  essential  that,  during  vulcani- 
zation, a  close  watch  is  kept  of  the 
temperature.  A  few  years  ago,  al- 
though it  was  known  that  it  was  the 
temperature  which  effected  the 
change,  yet  because  the  heat  was  de- 
rived from  steam,  which  was  meas- 
ured in  pounds  per  square  inch, 
steam  pressure  was  the  method  of 
control  used  in  vulcanizing  rubber. 
This  led  to  many  very  bad  results. 
For  instance,  in  a  vulcanizer,  you 
might  have  the  desired  pressure  of  45 
pounds  indicated  by  your  pressure 
gage  and  yet  there  might  be  pocketed 
air  at  some  place  in  the  heater  which 
is  not  at  the  desired  temperature  and 
faulty  goods  would  result. 

There  is  no  excuse  for  such  trouble 
today  when  it  is  possible  to  obtain 
automatic,  self-recording  thermom- 


CH3  •  C       CH2 


2  •  CH 


CH-CH2-CH2-C  —  CH, 

eters  like  those  put  out  by  the  C.  J. 
Tagliabue  Co.  or  those  of  the  Bristol 
Co. 

What  really  takes  place  during  vul- 
canization, or  in  other  words,  the 
chemistry  of  what  causes  this  marked 
change  in  the  properties  of  the  rub- 
ber, was  not  investigated  to  any  great 
extent  until  1902  to  1910.  Up  to  this 


C  — CH2CH2  CH         S 
CH  •  CH2  CH2   C       Cl 
CH, 


ories  of  vulcanization  which  later 
came  in  for  their  amount  of  criti- 
cism. We  shall  here  bring  forth  the 
main  points  which  he  developed. 

Previous  to  this  time  the  impres- 
sion had  existed  that  when  rub- 
ber was  mixed  with  sulphur  and  then 
heated,  substitution  took  place. 
Weber  showed  conclusively  that  this 
was  incorrect  for  he  pointed  out  that 
if  this  were  true,  an  immense  volume 
of  hydrogen  sulphide  must  be  pro- 
duced, which  is  contrary  to  our  work- 
ing experience.  Thus  the  substitu- 
tion theory  was  abandoned  and  in  its 
stead,  Weber  recommended  the  addi- 
tion theory.  According  to  that  the- 
ory if  we  accept  the  formula  for 
caoutchouc  as  recommended  by  Har- 
ries, we  have  a  compound  with  double 
bonds  at  which  points  addition  is 
possible. 

CH.-C     CH.-CH, 


S 


o 


\ 
CH-CH, 


f  CH2-C-CH3 

This  will  stand  for  rubber  com- 
pletely saturated  or  hard  rubber 
which  has  a  constant  per  cent  of  sul- 
phur of  approximately  32.  This 
same  reaction  takes  place  in  the  cold 
cure,  only  Hinrichsen  has  pointed  out 
that  the  reaction  undoubtedly  takes 
place  between  two  such  molecules 
thus: 

CH3 

•  S         CH  •  CH,  •  CH,       C 

I    +      II  li 

Cl         C — CH2-CH2-CH 

CH3 

CH, 


CH3 
C  —  CH2  CH2  CH  —  S  —  S  —  CH  •  CH2  •  CH2  —  C 

CH  —  CH2-CH3-C  —  Cl 
CH, 


Cl  —  C  —  CH2  •  CH2  •  CH 
CH 


time,  the  process  had  been  regarded 
as  purely  a  chemical  phenomenon. 

Weber's  Theory 

The  early  work  of  a  scientific 
nature  along  this  line  was  conducted 
by  Weber  and  he  laid  down  the- 


Weber  pointed  out  that  the  amount 
of  sulphur  which  actually  entered 
into  vulcanization  was  dependent  to 
some  extent  on  many  factors,  most 
important  of  these,  however,  being 
the  amount  of  sulphur  really  present 
and  capable  of  entering  into  the  re- 
action, and  second  the  temperature  at 


THEORIES  OF  VULCANIZATION 


101 


which  the  vulcanization  was  taking 
place,  and  third  the  length  of  time  it 
was  subjected  to  this  temperature. 
By  varying  these  conditions,  we  ob- 
tain different  degrees  of  vulcaniza- 
tion ranging  from  a  soft  consistency 
up  to  hard  rubber  for  ebonite. 

In  order  to  have  some  scale  for 
•comparing  this  degree  of  vulcaniza- 
tion, Weber  suggested  the  term  "  co- 
efficient of  vulcanization."  That  is, 
in  all  grades  of  cured  rubber,  we  have 
sulphur  in  at  least  three  modifications. 
There  is  "  total  sulphur,"  "  free  sul- 
phur ' '  and  ' '  combined  sulphur. ' '  the 
latter  being  the  amount  of  sulphur 
which  is  in  combination  with  caout- 
chouc. It  is  the  ratio  of  this  sulphur 
to  the  total  amount  of  rubber  present 
in  the  finished  product  which  is  called 
the  coefficient  of  vulcanization. 

The  unfortunate  thing  about  the 
use  of  this  is  the  fact  that  the 
same  coefficient  of  vulcanization  with 
different  grades  of  rubber  produces 
entirely  different  results,  and,  in 
fact,  different  results  in  the  same 
rubber  if  it  is  handled  in  different 
ways.  "Weber  came  to  the  conclu- 
sion that  this  range  of  vulcanization 
from  soft  rubber  to  ebonite  could  be 
represented  by  the  formation  of  ten 
sulphur  compounds  with  caoutchouc, 
the  lowest  having  a  formula  of 
(C10H16)10  S2  and  the  highest  ex- 
pressed by  the  formula  C,0H1BS2. 
As  proof  of  this  he  found  that  when 
determining  the  combined  sulphur 
in  samples  cured  for  different  lengths 
of  time  with  an  excess  of  sulphur 
present  and  then  plotting  the  com- 
bined sulphur  with  its  per  cent 
on  one  axis  and  time  expressed  on 
the  other,  he  obtained  a  broken  curve 
which  he  took  as  evidence  of  a  chem- 
ical change  taking  place.  These  are 
the  points  adduced  by  "Weber  in 
support  of  his  theory.  We  shall  now 
give  a  brief  review  of  the  theory  of 
W.  Oswald  concerning  vulcanization. 

Oswald's  Theory 

W.  Oswald  was  of  the  opinion  that 
vulcanization  might  be  explained  bet- 
ter upon  the  grounds  of  the  physico- 
chemical  theory  of  absorption  deal- 
ing with  colloids  than  upon  Weber's 
purely  chemical  theory. 

This  theory  of  Oswald's  is  found 


in  Z.  Chem.  Ind.  Kolloide,  1910,  6, 
136-155,  as  it  may  be  applied  to  vul- 
canization, and  he  points  out  the  fol- 
lowing facts  in  support  of  his  theory : 

First — Regardless  of  the  amount 
of  sulphur  added  to  rubber,  whether 
large  or  small,  there  always  remains 
after  vulcanization  a  £ertam  amount 
of  it  in  the  free  state,  V^djtjie'.iljem-'! 
ical  theory  would/' require,  Othat  .if 
small  in  amount,  J»\t  /should  i^afli  b$ 
combined. 

Second — If  vulcanized  rubber  is 
extracted  with  petroleum  spirit,  sul- 
phur will  continue  to  be  removed  as 
long  as  any  remains  in  the  rubber 
and  this  same  is  true  of  unvulcanized 
rubber  only  the  sulphur  is  extracted 
more  rapidly. 

Third — The  adsorption  of  sulphur 
by  rubber  is  always  additive. 

Fourth — A  continuous  series  of  ad- 
ditive products  is  formed  and  yet 
the  amount  of  sulphur  in  the  series 
does  not  conform  to  the  law  of  mul- 
tiple proportions. 

Fifth — The  amount  of  adsorbed 
sulphur  will  depend  upon  the  previ- 
ous mechanical  working  of  the  rub- 
ber. The  more  the  mechanical  work- 
ing, the  greater  the  amount  of  sur- 
face produced  and  thus  the  greater 
the  adsorptive  power  of  the  rubber. 

Sixth — The  adsorption  increases 
with  rise  of  temperature  and  con- 
forms more  nearly  to  what  should  be 
expected  from  a  physico-chemical  ad- 
sorption than  from  a  chemical  change 
alone. 

Seventh — The  adsorption  of  sul- 
phur is  not  regular  as  the  sulphur 
curve  shows  changes  in  direction. 

Eighth — The  adsorbtion  of  sul- 
phur proceeds  more  nearly  according 
to  the  adsorbtion  formula  than  to  any 
chemical  one.  That  is, 

—  =  kcm 
a 

Where  x  =  amt.  of  adsorbed  sub- 
stance, 

a  =  amt.  of  adsorbent. 

c  =  initial  concentration  of 
substance  which  is  ad- 
sorbed. 

k  and  m  are  constants. 

From  these  facts.  Oswald  concludes 


102 


RUBBER   MANUFACTURE 


that  vulcanization  is  to  be  consid- 
ered as  an  adsorption  of  the  sulphur 
by  the  rubber.  Hinrichsen  and  E. 
Kindscher  studied  the  reaction  which 
takes  place  during  cold  vulcanization 
(Z.  Chem.  Ind.  Kolloids,  1910,  4). 
They  prepared  a  solution  of  rubber 
in  benzine,  using  a  known  quantity 
_of  tubW^^jTo  this  they  added 
a  known 'quantity  of  sulphur  mono- 
xjhloL'id^JdipSfJxved' in  benzine  and  al- 
ioweci  We  '  two  "  to  react  for  three 
weeks.  At  the  end  of  this  time,  they 
determined  the  amount  of  unchanged 
sulphur  monochloride  and  by  dif- 
ference they  ascertained  the  amount 
which  had  reacted  with  the  known 
amount  of  rubber.  They  came 
to  the  conclusion  that  for  a  certain 
amount  of  rubber,  the  amount  of  ad- 
sorbed monochloride  is  constant  and 
is  independent  of  the  amount  taken. 
They  then  calculated  a  formula  for 
this  final  compound  which  they  wrote 
as  indicated  above  (C10H16)2  S2  C12. 
This  work  seems  to  favor,  therefore, 
the  idea  of  a  chemical  change  during 
vulcanization  but  Oswald  pointed  out 
that  this  simply  represented  the 
maximum  amount  of  adsorbed  sul- 
phur and  represented  that  part  of 
the  sulphur  curve  which  was  parallel 
to  the  axis. 

These  same  men  later  carried  out 
the  following  test  with  hot  vul- 
canization. They  prepared  a  solu- 
tion of  rubber  in  cumene  of  such  a 
concentration  that  each  100  c.c.  of 
the  solution  contained  two  grams  of 
rubber.  To  several  such  amounts 
they  added  1,  2,  3,  4,  5,  6,  7  and  8 
grams  of  sulphur  respectively.  The 
mixtures  were  then  all  subjected  to  a 
temperature  of  170  deg.  C.,  while 
being  agitated  by  carbon  dioxide.  In 
each  case,  the  product  which  resulted 
did  not  contain  more  than  32  per 
cent  of  sulphur  and  therefore  agreed 
with  Weber's  formula  of  C10H16  S2 
showing  that  here  perhaps  is  a  chem- 
ical compound  capable,  therefore,  of 
being  represented  by  a  formula. 

Following  the  appearance  "of  Os- 
wald's theory  we  find  a  great  deal  of 
investigation  and  discussion  along 
this  line. 

Spence's  Experiment 
Spence    and    his    workers    in    this 


country  did  a  great  deal  of  work  on 
this  theory  of  vulcanization.  For  in- 
stance, they  studied  the  velocity  with 
which  free  sulphur  is  extracted  from 
vulcanized  rubber  by  use  of  hot  ace- 
tone and  came  to  the  conclusion  that 
the  last  portions  of  free  sulphur  are 
removed  very  slowly  but  that  a  point 
is  reached  where  no  more  sulphur 
may  be  removed.  Therefore,  in  con- 
tradiction to  Oswald's  theory,  they 
claimed  that  a  definite  amount  of  sul- 
phur had  really  entered  into  chem- 
ical union  with  the  rubber  during 
vulcanisation.  They  do,  however, 
agree  with  Oswald  in  that  they  be- 
lieve that  the  free  sulphur  may  be  ad- 
sorbed. 

Reversability   of    Vulcanization   Process 

P.  Bary  and  L.  Weydert  (Comptes 
Rend.,  1911,  153,  676-679)  did  a  piece 
of  work  to  prove  that  the  process 
which  takes  place  during  vulcaniza- 
tion was  one  which  might  be  reversed. 
They  extracted  some  vulcanized  rub- 
ber with  hot  acetone  until  all  free  sul- 
phur was  removed  and  then  heated 
the  extracted  rubber  for  eight  hours 
at  145  deg.  C.  in  carbon  dioxide.  Fol- 
lowing this  they  extracted  again  with 
hot  acetone  and  repeated  the  previous 
treatment  twice  more  with  the  result 
that  the  final  amount  of  combined 
sulphur  was  less  than  in  the  orig- 
inal sample.  Therefore,  they  felt 
that  they  had  reversed  the  process 
of  vulcanization  to  a  certain  extent. 
This  is  a  very  important  point  in  the 
controversy  for  if  vulcanization  may 
be  reversed,  it  lends  great  weight  to 
the  adsorption  theory,  while,  on  the 
other  hand,  if  it  is  impossible  to  re- 
verse the  process,  then  it  argues  in 
favor  of  Weber's  theory.  They  were 
also  of  the  opinion  that  during  vul- 
canization, the  rubber  itself  was  de- 
polymerized. 

Migration  of  Sulphur  in  Rubber 

H.  Skellon  has  carried  out  some 
experiments  dealing  with  the  migra- 
tion of  sulphur  in  rubber  during  vul- 
canization. He  superimposed  two 
sheets  of  rubber  containing  different 
percentages  of  sulphur  and  then  sub- 
jected them  to  vulcanization  condi- 
tions and  came  to  the  following  con- 
clusions : 


THEORIES  OF  VULCANIZATION 


103 


That  migration  takes  place  either 
upward  or  downward  with  equal 
facility. 

That  equilibrium  is  very  quickly 
arrived  at  in  the  two  sheets  during 
vulcanization,  and  then  the  concen- 
tration of  the  free  sulphur  in  the  rub- 
ber is  the  same  in  the  two  sheets. 

That  the  evidence  points  to  the 
fact  that  vulcanization  is  most  prob- 
ably 

(1)  Melting  of  the  sulphur; 

(2)  Solution    of    the    sulphur    in 
rubber ; 

(3)  Slow  combination  of  the  sul- 
phur with  the  rubber. 

Skellon  made  a  study  of  the  effect 
of  the  polyprene  sulphide  during  vul- 
canization and  came  to  the  follow- 
ing conclusions: 

Let  us  picture  vulcanization  to  be 
represented  by  the  following  reaction 

(C10H18)n+  NS2<— >NC10H16S2 
If  this  is  true,  we  should  expect  that 
during  vulcanization,  the  ratio  of 
rubber  to  sulphur  remains  the  same 
and  therefore  the  reaction  should  pro- 
ceed at  the  same  rate  of  speed,  but  by 
actual  experiment,  this  is  found  not 
to  be  the  case.  The  speed  of  vulcani- 
zation is  decreased  as  the  process  goes 
on.  This  is  explained  by  Skellon  to 
be  due  to  the  fact  that  sulphur  is 
more  soluble  in  polyprene  sulphide 
than  in  rubber  and  therefore  the  law 
of  partition  comes  in  and  we  actually 
have  some  of  the  sulphur  extracted 
from  the  rubber  by  the  sulphide 
which  is  formed,  hence  more  sulphur 
will  be  dissolved  by  it  and  the  last 
stages  of  the  cure  will  proceed  very 
slowly  as  a  result  of  this. 

Researches  by  Loewen 

H.  Loewen  has  carried  out  a  very 
interesting  experiment  favoring  the 
idea  that  the  process  of  vulcanization 
consists  in  the  sulphur's  first  dissolv- 
ing in  the  rubber  and  then  combining 
chemically  with  it,  in  contrast  to  the 
adsorption  theory  of  Oswald. 

To  study  this  phenomenon,  he 
placed  a  small  amount  of  rubber  with 
10  per  cent  of  its  weight  of  sulphur 
on  a  microscope  slide  and  placed 
over  it  a  cover  glass.  This  slide  he 
then  subjected  to  a  temperature  of 


130  deg  to  140  deg.  C.,  and  at  regu- 
lar intervals  made  microscopic  exami- 
nations of  it. 

At  first  the  sulphur  melted  and  the 
globules  could  be  seen  through  the 
rubber  itself,  later  the  globules  dis- 
tributed themselves  throughout  the 
whole  mass  and  by  continued  heating, 
the  whole  mass  became  clear  or  trans- 
parent, but  he  observed  further  that 
as  this  cooled,  it  became  cloudy  due 
to  the  separating  out  of  the  globules 
of  rubber  which,  as  we  know,  change 
back  in  cooling  to  the  rhombic  form. 
Then,  again,  if  the  slide  is  heated 
until  upon  cooling  it  still  remains 
clear,  then  when  the  excess  sulphur 
does  separate  it  will  do  so  in  the 
crystalline  form  and  not  appear  as 
globules  first  thus  resembling  solu- 
tions. He  also  found  that  sulphur  is 
more  soluble  the  higher  the  degree  of 
vulcanization  and  calls  attention  to 
the  fact  that  hard  rubber  does  not 
tend  to  bloom  even  though  it  may 
have  a  large  per  cent  of  free  sulphur. 
This  is  explained,  therefore,  on  the 
ground  that  the  sulphur,  being  more 
soluble,  here  remains  in  solution.  He 
then  placed  some  rubber  alone  on  a 
slide  and  placed  over  it  the  cover 
glass  and  around  the  edges  of  the  rub- 
ber he  placed  molten  sulphur.  After 
regular  intervals  of  heating,  he  would 
examine  it  with  the  microscope  and 
found  that  the  sulphur  diffused  into 
the  rubber  to  some  distance  as  would 
be  expected  during  solution  of  one 
in  the  other. 

These  experiments  led  Loewen  to 
the  firm  belief  that  vulcanization  was 
truly  a  chemical  process.  (Gummi- 
Zeit.  1913,  27,  1301-1302.) 

Vulcanization  and  Viscosity 

Dr.  Gustave  Bernstein  in  a  report 
before  the  Eubber  Congress,  held  in 
London,  1914,  showed  how  he  had 
studied  vulcanization  from  the  stand- 
point of  viscosity.  He  is  of  the  opin- 
ion that  rubber  must  be  depolymer- 
ized  before  it  can  enter  into  chemical 
change,  that  is,  it  must  change  phys- 
ically from  (C10H16)n  to  NC10H16. 
All  of  the  agents  which  will  depol- 
merize  rubber  will  also  reduce  its  vis- 
cosity. He  also  observed  that  the  vis- 
cosity of  all  completely  depolymer- 
ized  rubber  was  the  same.  He  also 


104 


RUBBER   MANUFACTURE 


called  attention  to  the  fact  that  all 
the  physical  agents  that  bring  about 
•depolymerization,  cause  a  vulcaniza- 
tion action  to  take  place  when  the 
rubber  is  mixed  with  sulphur.  An 
example  of  this  is  seen  when  a  so- 
lution of  rubber  and  sulphur  is  ex- 
posed to  the  ultra-violet  rays.  Its 
viscosity  immediately  increases.  If 
this  is  true,  then  our  vulcanization  is 
to  be  explained  upon  the'  ground  that 
the  heat  first  depolymerizes  the  rub- 
ber and  then  the  sulphur  repoly- 
merizes  it. 

In  support  of  this  theory,  he  points 
out  the  fact  that  while  mixing  sul- 
phur and  rubber  on  the  rolls  at  a 
temperature  not  exceeding  80  deg.  C, 
vulcanization  took  place  and  by  an- 
alysis, 0.8  per  cent  of  combined  sul- 
phur was  found,  while  upon  heating 
the  same  mixture  in  an  oven  at  80 
deg.  C  for  the  same  length  of  time 
no  combined  sulphur  was  found. 

The  conclusion  to  be  drawn  is  that 
the  mechanical  work  assisted  the  de- 
polymerization  of  the  rubber  and  the 
sulphur  then  entered  into  combina- 
tion. Then  if  this  be  true,  the  sul- 
phur must  act  partly  at  least  jn  the 
capacity  of  a  catalytic  agent.  That 
this  is  true  follows  from  the  work  of 
Helbronner  where  he  found  that 
.actinic  light  had  really  vulcanized 
the  solution  of  rubber  and  sulphur 
and  yet  the  amount  of  combined  sul- 
phur was  only  0.6  per  cent.  This 
fact  is  still  borne  out  by  the  addition 
of  a  small  amount  of  sulphur  to  aid 
in  the  polymerization  of  isoprene  to 
produce  synthetic  rubber  by  the 
Badische  Anilin  process.  The  rub- 
ber obtained  by  this  process  is  poly- 
merized more  highly  than  the  nat- 
ural rubber. 

He  therefore  draws  the  following 
conclusions:  first,  that  what  we  call 
vulcanization  is  a  repolymerization ; 
second,  smaller  quantities  of  sulphur 
than  are  ordinarily  used  are  capable 
of  effecting  this  change ;  third,  the 
amount  of  combined  sulphur  is  not 
necessarily  a  measure  of  the  degree 


of  vulcanization  as  claimed  by  C.  0. 
Weber. 

The  following  idea  has  also  been 
brought  forward.  As  we  know  cer- 
tain physical  agencies  have  the  power 
of  lowering  the  viscosity  of  rubber 
and  this  points  to  its  depolymeriza- 
tion. However,  the  action  of  physical 
agencies,  like  ultra-violet  rays,  upon 
sulphur  in  solution  is  to  polymerize  it 
and  thus  make  it  into  an  insoluble 
colloidal  form.  Therefore,  vulcaniza- 
tion is  first  depolymerization  of  the 
rubber  and  at  the  same  time  polymeri- 
zation of  the  sulphur  and  then  we 
may  think  of  the  depolymerized  rub- 
ber as  adsorbing  the  colloidal  sulphur. 

Upon  this  theory  we  might  explain 
the  deterioration  of  rubber  under  the 
influence  of  certain  physical  agencies 
as  due  to  the  continuation  of  the  de- 
polymerization  of  the  rubber  and  the 
increased  polymerization  of  the  sul- 
phur. 

Ostromislensky's  Theory 

I.  I.  Ostromislensky  has  recently 
advanced  what  may  be  looked  upon 
as  a  combination  theory  made  up  of 
the  two  others.  He  suggested  that 
vulcanization  consisted  first  in'  a 
small  amount  of  sulphur  forming  a 
derivative  with  the  caoutchouc  which 
may  be  regarded  as  the  vulcanizing 
substance,  second  this  substance  is 
then  adsorbed  by  the  remaining  rub- 
ber and  the  whole  mass  is  regarded  as 
vulcanized.  Thus  it  will  be  seen  that 
it  is  first  a  chemical  change  and  then 
an  adsorptive  process.  It  is  in  this 
state  of  reasoning  and  theorizing  that 
we  find  ourselves  today. 

From  work  carried  out  in  this 
laboratory,  we  have  come  to  the  be- 
lief of  Spence  that  it  is  a  chemical 
change  and  that  when  accurate  de- 
terminations of  the  combined  sulphur 
are  made  on  samples  taken  at  short 
intervals  of  time,  the  sulphur  curve 
will  become  a  smooth  one  without  the 
kinks  in  it  which  Weber  found,  and 
may  thus  be  looked  upon  as  a  true 
chemical  change. 


CHAPTER  XVI 
Methods  of  Reclaiming  Rubber 


In  tliis  section,  we  shall  consider 
the  different  ways  in  which  rubber 
which  has  been  once  used  may  be 
treated  and  thus  returned  to  com- 
pounds. 

This  of  course  includes  a  great 
many  different  processes  because  of 
the  great  variety  of  compounds  or 
stocks  which  furnish  the  material  to 
be  reclaimed  and  then  too  the  great 
number  of  stocks  into  which  the 
shoddy  may  be  worked. 

We  shall  have  therefore  as  raw  ma- 
terial which  is  to  be  reclaimed,  first, 
unvulcanized  stock  in  the  form  of 
trimmings.  This  may  have  in  it  fab- 
ric, mineral  fillers  and  its  free  sul- 
phur. Second,  the  vulcanized  stock, 
ranging  in  degree  of  vulcanization 
from  soft  cure  up  to  hard  cure  or 
ebonite.  These  materials  may  contain 
fabric,  fillers,  and  even  metal  as  we 
find  the  metal  beads  in  tires,  free 
sulphur  and  substitutes.  Third,  we 
have  hard  rubber  waste  itself. 

The  first  class  of  material  very  sel- 
dom comes  into  the  hands  of  the  re- 
claimer proper  for  being  unvulcan- 
ized.  All  that  is  necessary  is  to  treat 
the  waste  with  a  rubber  solvent  like 
naphtha.  A  great  deal  of  the  waste 
does  not  contain  even  fabric,  but 


CH,  —  C  —  CH,  CH,  —  C  —  H 

/  ( 

\ 

S 

S 

\ 

/ 

CH— CH2  CH2  —  C  —  CH3 

simply  the  rubber  plus  the  sulphur 
and  mineral  fillers,  and  when  the 
solution  is  effected,  the  naphtha  solu- 
tion is  wrung  out  of  the  fabric  if  it 
is  present,  and  if  absent  it  is  decanted 
from  the  mineral  matter.  The  solvent 


is  then  evaporated  and  the  rubber  is 
thus  reclaimed.  This  is  a  very  simple 
process,  and,  although  strictly  speak- 
ing it  is  a  form  of  reclaiming,  yet  it 
is  one  that  is  not  regarded  as  such 
in  the  reclaiming  industry. 

The  big  problem  that  confronts  the 
reclaimer  is  the  handling  of  the  sec- 
ond class  of  materials,  namely  that 
which  has  been  vulcanized  and  thus 
had  some  of  its  chemical  and  physical 
properties  changed  by  some  of  the 
sulphur  having  entered  into  chemical 
union  with  the  caoutchouc. 

Therefore  every  man  when  he  ap- 
proaches the  problem  does  so  with 
the  idea  that  he  will  be  able  to  find 
a  process  whereby  the  original  hydro- 
carbon will  be  found  again  in  a  form 
capable  of  the  same  degree  of  vul- 
canization that  it  possessed  before  it 
ever  went  into  a  rubber  compound. 
In  fact  he  tries  to  split  off  the  sul- 
phur atoms  in  the  vulcanized  mole- 
cule and  thus  go  back  to  the  un- 
saturated  hydrocarbon. 

This  might  be  represented  as  the 
reverse  of  the  action  which  took  place 
during  vulcanization  and  might  be 
called  devulcanization. 

This  would  represent  the  process 
in  tl)e  case  of  ebonite.  That  this 

CH,  —  C  —  CH,    CH,  —  CH 


CH— CH2    CH2  —  C  —  CH3 

goal  has  never  been  reached  and  that 
it  is  not  probable  that  it  will  be 
reached  seems  apparent  today. 

The  formula  C10H16S2  as  we  have 
mentioned  before  represents  hard 
rubber,  yet  the  rubber  which  has  been 


105 


106 


RUBBER   MANUFACTURE 


subjected  to  reclaiming  contains  much 
less  combined  sulphu?  than  this 
formula  indicates. 

The  above  formula  contains  ap- 
proximately 32  per  cent  of  sulphur, 
while  the  material  used  by  the  re- 
claimer will  average  about  3  per 
cent  or  even  less.  It  would  appear 
therefore  that  a  large  part  of  the  rub- 
ber is  not  vulcanized  and  that  all  that 
would  be  necessary  to  obtain  the  un- 
vulcanized  rubber  would  be  to  treat 
the  product  with  a  suitable  solvent, 
then  evaporate  it  off  and  the  rubber 
would  thus  be  obtained.  But  this  is 
not  the  case,  for  the  combined  sul- 
phur and  the  product  in  which  it 
exists  are  very  securely  bounded  and 
held  together. 

However,  to  effect  the  above  men- 
tioned change  many  patents  have 
from,  time  to  time  appeared,  many  of 
which  have  never  been  put  into  prac- 
tice and  many  of  which  have  been 
allowed  to  lapse.  We  shall  simply 
mention  some  of  these  and  when 
doing  so  will  classify  them  as  to 
whether  they  are  purely  mechanical 
processes  or  chemical  ones.  The  latter 
may  be  either  ' '  Acid  "  or  "  Alkali. ' ' 

De-vulcanization   Processes 

In  1857,  Conrad  Poppenhusen  and 
Ludwig  Held  suspended  finely  di- 
vided rubber  in  different  solvents  and 
then  conducted  into  this  mixture  dry 
ammoniacal  gas.  The  gas  is  absorbed 
and  the  gum  swells,  the  whole  mass 
becomes  viscid,  and  this  material  is 
then  suitable  to  be  used  in  new  com- 
pounds. 

One  of  the  oldest  methods  was  pre- 
sented by  Hiram  L.  Hall  in  1858. 
In  this  process  the  vulcanized  rubber 
was  boiled  up  with  water  in  a  caldron 
after  it  had  been  reduced  to  a  finely 
divided  state  to  make  it  semi-plastic. 
It  could  then  be  put  into  compounds 
again. 

In  1860,  Edward  Simon  patented 
a  process  in  which  he  subjected  one 
hundred  parts  of  shredded  waste 
vulcanized  India  rubber  and  two 
parts  of  chloride  of  lime  to  an  open 
heat  at  a  temperature  of  1000  deg.  to 
1100  deg.  F.  The  rubber  melted  and 
during  constant  stirring  the  sulphur 
was  distilled  out.  The  plastic  mass 


which  remained  could  then  be  worked 
into  new  stocks. 

In  1861,  John  Murphy  took  out  a 
patent  for  the  reclaiming  of  rubber 
whereby  the  old  rubber  was  mixed 
with  sulphur  and  vulcanized  until  it 
formed  hard  stock.  This  was  then 
formed  hard  stock.  This  was  reduced 
to  a  powder  and  then  mixed  with 
unvulcaiiized  gum  and  made  into 
whatever  form  was  desired  and  this 
vulcanized.  This  was  a  peculiar  man- 
ner, to  say  the  least,  of  using  waste 
rubber. 

In  the  same  year,  Charles  Mc- 
Burney  patented  the  idea  that  by 
mixing  old  vulcanized  rubber  which 
had  been  reduced  to  a  fine  state  with 
oils  like  pine  or  rosin  oil,  cottonseed 
oil,  olive  oil,  castor  oil,  palm  oil,  or 
cocoanut  oil,  and  allowing  it  to  stand 
for  several  hours,  then  by  adding  raw 
rubber  and  the  necessary  fillers  for 
which  the  product  is  intended,  the 
material  may  be  all  incorporated  on 
a  mill  and  vulcanized.  It  thus  af- 
fords a  way  of  using  old  rubber. 

Thomas  J.  Mayall  in  1862  proposed 
that  vulcanized  rubber  waste  might 
be  rendered  fit  for  use  again  by  grind- 
ing the  material  to  a  fine  powder.  He 
then  made  up  a  batch  composed  of 
five-eighths  of  this  old  rubber  and 
three-eighths  of  a  vegetable  oil  or 
pine  oils  and  mixed  them  thoroughly 
on  a  mill.  This  material  was  then 
subjected  to  a  gentle  heat. 

In  1863,  Alfred  Ford  patented  in 
England  a  process  in  which  the  old 
rubber  is  boiled  with  a  strong  solu- 
tion of  alkali;  the  material  is  then 
powdered  and  placed  in  moulds  which 
are  subjected  to  a  hydraulic  pressure 
and  heat  of  ordinary  vulcanization  by 
which  the  whole  will  be  agglutinated. 

In  1863,  Charles  H.  Hayward  pat- 
ented what  may  be  regarded  as  the 
acid  process  of  today. 

In  1871,  H.  Smyser  brought  out  a 
patent  for  the  using  of  old  rubber  by 
simply  reducing  it  to  a  fine  powder 
on  a  grindstone  and  then  incorporat- 
ing this  dust  into  a  new  compound. 

In  1881,  N.  C.  Mitchell  defended 
by  patent  what  are  known  as  the  acid 
processes. 

He     reduced    the     rubber    to     be 


METHODS  OF  RECLAIMING  RUBBER 


107 


treated  to  a  fine  state  of  division,  then 
placed  it  in  a  tight  steam  box  in 
which  a  steam  pressure  of  from  50 
to  75  Ib.  could  be  maintained.  Into 
this  box  containing  the  rubber  he 
placed  sulphuric  acid  or  muriatic 
acid  of  varying  strength,  depending 
upon  the  grade  of  compound  to  be 
treated.  Then  the  whole  was  closed 
and  the  steam  turned  on  for  from 
one  to  five  hours.  The  rubber  was 
then  removed,  washed  and  dried. 
This  treatment  of  course  removes 
fabric  from  the  compound  as  well  as 
mineral  fillers  which  are  used. 

McDermott  in  1882  modified  the 
Mitchell  acid  process  a  little  by  add- 
ing alone  with  the  charge  of  acid  and 
rubber  some  manganese  dioxide  and 
a  solution  of  potassium  bichromate. 
Then  he  subjected  the  whole  to  steam 
under  pressure,  the  result  being  prac- 
tically the  same. 

In  1883,  A.  W.  Kent  patented  an 
apparatus  for  the  washing  of  ground 
rubber  on  a  sieve,  thus  allowing  the 
dirt  and  sand  to  be  washed  away, 
also  the  fiber,  and  allowing  simply  the 
vulcanized  rubber  with  its  fillers  to 
remain.  This  is  dried  and  as  such  is 
mixed  with  new  compounds. 

In  1883,  John  L.  Chadwick  pat- 
ented a  process  for  removing  both 
cotton  and  wool  fabric  from  vul- 
canized rubber.  The  scrap  is  first 
immersed  in  muriatic  acid  of  10  deg. 
Baume  and  then  heated  to  from  200 
deg.  to  212  deg.  F.  This  continues 
for  a  couple  of  hours,  when  the  cotton 
is  destroyed.  The  material  is  then 
wrung  out  of  the  acid  and  passed 
through  a  wool  picker.  Not  all  of 
the  wool  is  removed  in  this  way,  so 
it  is  then  placed  in  a  22  deg.  Baume 
solution  of  caustic  soda.  Before  this 
all  the  acid  must  be  removed  by  Avash- 
ing.  When  removed  from  the  soda 
solution  and  washed,  it  is  in  a  good 
workable  form. 

In  1884,  J.  J.  Montgomery  sub- 
jected vulcanized  rubber  to  the  action 
of  hydrocarbons  obtained  from  pe- 
troleum, that  have  boiling  points 
around  400  deg.  to  450  deg.  F.,  at 
a  temperature  of  350  deg.  F.  The 
rubber  becomes  a  doughy  or  plastic 
mass  from  which  the  oils  are  removed 
by  heat. 


In  1890,  N.  C.  Mitchell  patented 
a  new  modification  in  which  the  rub- 
ber after  it  had  been  ground  and 
washed  is  heated  with  steam  in  the 
presence  of  calcium  sulphide  to  which 
has  been  added  some  heavy  petroleum 
which  keeps  the  rubber  in  a  moist 
condition. 

Maximilien  Gerber  in  1894  pro- 
tected his  process  of  reclaiming  by 
a  patent  whereby  the  rubber  scrap  is 
heated  in  a  double  bottomed  closed 
vessel  with  a  solvent  for  the  gum 
along  with  a  metal,  in  the  finely  di- 
vided condition,  which  has  a  great 
affinity  for  sulphur.  Such  metals  are 
iron,  tin,  lead,  zinc,  mercury,  etc.,  and 
the  solvent  being  benzine,  carbon 
tetrachloride  and  the  like. 

The  charge  is  heated  to  from  139 
deg.  to  144  deg.  C.  for  about  eight 
hours;  then  it  is  allowed  to  stand  in 
a  receiver  for  twenty-four  hours, 
when  the  sulphides  and  fillers  will 
have  settled  out  and  the  rubber  solu- 
tion is  decanted.  The  rubber  is  ob- 
tained by  evaporating  the  solvent  or 
as  a  solution  is  used  to  waterproof 
cloth. 

In  1899,  A.  H.  Marks  patented 
what  is  known  as  the  alkali  process. 
By  this  .method  the  ground  rubber 
waste  is  brought  to  a  temperature  of 
344  deg.  to  370  deg.  F.  in  a  3  per 
cent  solution  of  caustic  soda.  This 
is  effected  in  a  closed  tank,  and  after 
a  period  of  about  twenty  hours  the 
process  is  completed,  when  the  rubber 
is  removed,  washed  and  dried.  This 
removes  the  free  sulphur,  the  fabric 
and  many  of  the  fillers  like  lead  com- 
pounds and  aluminum  ones.  In  1900, 
he  modified  his  patent  by  substituting 
a  rotating  cylinder  which  allowed  a 
better  mixing  during  the  treatment 
with  steam. 

In  1900,  Johan  Theilgaard  re- 
claimed waste  rubber  with  the  use  of 
potassium  cyanide,  but  this  is  too 
dangerous  a  process  to  be  recom- 
mended. 

In  1900,  Eobert  Cowan  patented 
a  machine  for  removing  foreign  mat- 
ter from  old  rubber.  Before  this 
time,  materials  like  nails,  leather, 
strings  and  bark  had  been  removed 
largely  by  washing.  His  machine  is 
what  is  known  as  a  strainer.  The 


108 


RUBBER   MANUFACTURE 


rubber  is  fed  into  a  machine  which, 
by  means  of  double  walls,  is  heated  by 
live  steam  to  a  temperature  where  the 
rubber  begins  to  soften  and  then  by 
a  worm  is  forced  through  the  strainer 
discs  which  retain  the  solid  particles 
but  allow  the  passage  of  the  rubber. 
This  machine  in  some  modified  form 
is  used  today  in  the  reclaiming  busi- 
ness in  connection  with  the  different 
processes  for  removing  the  iron. 
Along  with  it,  however,  a  powerful 
magnet  is  also  used  to  remove  iron 
particles.  In  1904,  L.  T.  Petersen 
modified  the  alkali  process  by  first 
treating  the  washed  and  shredded 
rubber  with  the  alkali  raised  only  to 
its  boiling  point.  After  the  fiber  is  re- 
moved, the  rubber  is  taken  from  this 
solution  and  treated  with  an  aqueous 
solution  of  a  hydrocarbon  or  oxy- 
hydrocarbon  such  as  phenol  under 
high  temperature  and  pressure.  The 
remaining  alkali  is  here  combined  and 
the  rubber  reclaimed  or  rendered 
workable. 

In  1908,  George  Capelle  reclaimed 
by  using  as  a  solvent  the  hydrocar- 
bons which  result  from  the  distilling 
of  India  rubber  in  vacuo. 

In  1909,  Auguste  Tixier  treated 
rubber  waste  with  terpeneol,  which 
dissolved  the  rubber,  and  then  he 
precipitated  it  by  the  addition  of  al- 
cohol. 

In  1910,  G.  S.  Heller  patented 
what  is  termed  the  Electric  Reclaim- 
ing Process.  The  rubber  is  first  re- 
duced to  a  fine  state  of  division  and 
is  then  charged  into  a  large  metal 
cylinder  which  may  be  stationary  and 
contain  agitating  paddles  on  the  in- 
side, or  it  may  be  a  rotating  drum 
thus  agitating  the  solution.  Around 
the  container  is  placed  a  large  band 
which  connects  with  one  of  the  poles 
of  a  generator,  and  into  the  center  of 
the  drum  projects  the  opposite  pole 
from  the  generator.  The  following 
charge  is  placed  in  the  retainer: 
100  Ibs.  of  ground  rubber,  600  Ibs.  of 
water,  21  Ibs.  of  sodium  hydroxide  and 
1  Ib.  of  ferric  sulphate.  The  retainer 
is  closed,  steam  is  turned  on  and  the 
contents  heated  to  from  330  deg.  to 
370  deg.  F.,  the  whole  agitated  and 
the  electric  current  will  also  flow 
through  this  electrolyte,  thus  its 


name.  The  process  requires  from  ten 
to  twenty-four  hours.  The  rubber  is 
removed,  washed,  and  dried.  In 
many  respects  the  product  resembles 
that  obtained  by  the  alkali  process. 

David  A.  Cutler  in  1913  recom- 
mended the  use  of  zinc  chloride  as 
a  solvent  for  the  fabric  in  the  place 
of  either  acid  or  alkali.  As  a  work- 
able charge  he  used :  35  Ib.  of  ground 
rubber;  87.5  Ib.  of  water;  17.5  oz. 
of  zinc  chloride ;  4  Ib.  6  oz.  of  oil, 
which  is  a  distillate  from  pine  wood. 
This  is  all  thoroughly  mixed  in  a  tank 
and  finally  heated  in  a  closed  vul- 
canizer  at  a  pressure  of  100  Ibs.  of 
steam.  The  rubber  is  removed  and 
washed. 

In  1913,  H.  W.  Kugler  modified  the 
alkali  process  by  adding  to  the  charge 
two  to  five  per  cent  of  aniline.  The 
charge  is  subjected  to  a  pressure  of 
from  60  to  150  Ibs.  of  steam  for  eight 
hours.  The  rubber  is  removed, 
washed  and  dried. 

In  1915,  Orrin  A.  Wheeler  patented 
the  following  process:  "The  im- 
proved method  of  treating  rubber 
scrap  containing  fiber  is  as  follows: 
The  scrap,  such  as  tires,  shoes,  hose, 
etc.,  is  ground  and  pulverized  in  the 
usual  manner.  The  pulverized  mate- 
rial is  then  treated  with  a  strong  solu- 
tion (about  20  per  cent)  of  caustic 
soda  and  allowed  to  stand  in  a  cool 
place  approximately  from  three  to 
five  hours.  Next  the  material  is 
placed  in  a  digester  which  is  equipped 
so  that  it  can  be  sealed  or  closed  up 
tightly,  and  carbon  disulfide  (CSo), 
about  one  pound  more  or  less  accord- 
ing to  the  character  of  the  material 
treated  to  about  ten  pounds  of  dry 
rubber  scrap,  is  added  to  the  material, 
and  then  the  digester  is  closed  and 
hermetically  sealed.  This  mixture  is 
permitted  to  remain  in  the  digester 
for  from  one  to  five  hours  to  permit 
chemical  reaction  to  occur,  the  di- 
gester being  operated  during  such  a 
period  to  stir  and  agitate  the  mass 
to  facilitate  the  said  reaction  and 
thereby  bring  about  a  combination  of 
the  sulphur  with  the  cellulose,  and 
so  producing  a  cellulose  Xanthoge- 
nate.  On  completion  of  this  reaction, 
the  rubber  and  fiber  are  converted 
into  a  sticky  cohesive  mass.  Next 


METHODS  OF  RECLAIMING  RUBBER 


109 


water  in  quantity  approximately 
equal  to  the  original  dry  rubber  is 
added  to  the  material  in  the  digester 
and  the  agitation  is  continued,  the 
water  mixing  with  the  cellulose  to 
distend  it.  Next  the  mass  in  the  di- 
gester is  heated  by  carefully  raising 
the  steam  pressure  in  the  heating 
chamber  around  the  digester  to  ap- 
proximately 100  Ibs.,  which  pressure 
is  kept  up  for  a  period  ranging  ap- 
proximately from  fifteen  to  twenty 
hours,  according  to  the  stock  under 
treatment,  and  during  such  time 
agitation  and  stirring  of  the  mass  will 
be  continued  a  part  of  or  all  the  time. 
This  heating  causes  the  cellulose  to 
become  insoluble  in  water  and  devul- 
canizes  the  rubber  in  the  presence  of 
caustic  soda  and  carbon  disulfide.  In 
this  process  carbon  disulfide  tends  to 
dissolve  the  combined  sulphur  and 
dissolves  all  the  free  sulphur,  and 
when  heated  produces  a  high  pressure 
in  the  digester,  thereby  causing  thor- 
ough impregnation  of  every  particle 
of  rubber  under  treatment  and  great- 
ly assisting  in  the  recovery  of  the 
rubber.  The  solvent  may,  of  course, 
be  recovered. 

In  this  method  of  reclaiming  rub- 
ber, the  cotton  fiber  that  is  usually 
destroyed  or  removed  in  other  proc- 
esses is  permitted  to  remain  with  the 
rubber  and  utilized  and  becomes  a 
valuable  ingredient  in  both  soft  and 
hard  rubber  compounds.  The  rubber 
and  elastic  tenacious  cellulose  unite 
and  intermingle  so  that  an  article 
made  therefrom  will  possess  the 
toughness  and  wearing  qualities  of 
new  and  pure  rubber  and  will  be  su- 
perior for  some  purposes,  particu- 
larly where  the  article  made  from  the 
reclaimed  product  is  to  be  subjected 
to  heat,  is  exposed  to  the  elements  or 
to  the  action  of  oils,  acids  and  al- 
kalis. Since  the  cellulose  of  the 
fibrous  material  in  the  scrap  is 
utilized  to  advantage  in  the  product, 
the  cost  is  less  than  under  any  pre- 
vious process  in  which  the  fiber  is 
destroyed  and  removed  or  removed 
without  being  destroyed. 

An  excellent  grade  of  material  can 
be  made  from  the  product  of  the 
process  with  the  addition  of  sulphur, 
and  with  the  addition  of  some  of  the 


cheaper  gums,  such  as  pontianiac, 
acra  flake,  guayule,  an  article  of  a 
higher  grade  can  be  produced  at  a 
low  cost.  If  desired  new  rubber  may 
be  added. 

A  comparatively  good  grade  of  re- 
claimed rubber  can  be  obtained  by 
introducing  the  alkali  and  carbon 
disulfide  at  the  same  time,  but  better 
results  are  believed  to  result  from  the 
successive  treatment  with  the  alkali 
and  carbon  disulfide  as  herein  before 
set  forth. 

The  invention  is  not  to  be  under- 
stood to  be  restricted  to  the  precise 
process  and  proportions  set  forth, 
since  these  may  be  modified  by  those 
skilled  in  the  art  without  departing 
from  the  spirit  and  scope  of  the  in- 
vention. 

In  1916,  Gray  Staunton  ground 
rubber  and  cleaned  it  of  fiber  by  a 
mechanical  process.  This  material  is 
then  mixed  in  the  proportion  of  80 
per  cent  waste  rubber  and  20  per 
cent  dry  potassium  carbonate.  The 
mixture  is  placed  on  trays  and  placed 
in  a  tight  heater  and  steam  admitted 
to  a  pressure  of  from  15  to  60  Ibs. 
The  sulphur  is  removed  as  K2S5  which 
is  soluble  in  water. 

Rubber  waste  may  be  worked  up 
with  linseed  oil  while  heating  and  the 
resulting  semi-liquid  mass  treated 
with  sulphur  monochloride  when  a 
so-called  rubber  substitute  is  pro- 
duced. 

In  the  above  we  have  not  men- 
tioned all  of  the  various  methods  that 
have  been  suggested  from  time  to 
time,  in  fact  very  few  of  the  patents 
have  been  mentioned,  but  we  have 
striven  to  give  types.  When  a  careful 
survey  is  made  of  all  of  these  and 
the  many  other  patents  also,  it  will 
be  perfectly  apparent  to  all  that 
there  are  only  about  two  methods, 
namely,  the  alkali  and  acid  processes, 
or  perhaps  a  combination  of  these 
two  into  one  called  the  acid-alkali 
method. 

Practically  all  patents  claim  to  be 
able  to  remove  all  of  the  sulphur  from 
the  rubber,  and  yet  the  fact  remains 
that  no  sulphur-free  shoddy  is  to  be 
obtained  on  the  market.  Therefore, 
there  is  a  limit  to  the  number  of  times 


110 


RUBBER    MANUFACTURE 


that  the  same  rubber  may  be  put 
through  the  reclaimer,  and  that  limit 
is  reached  in  ebonite  or  hard  rubber. 
Today  hard  rubber  is  generally  re- 
duced to  a  powder  and  incorporated 
into  compounds  simply  as  an  inor- 
ganic filler  might  be.  In  the  mind  of 
the  writer  the  most  important  thing 
in  the  reclaiming  business,  regardless 
of  the  method,  is  the  removing  of  the 
fabric  and  free  sulphur  at  as  low  a 
temperature  as  possible.  We  know 
that  alkalis  have  a  pronounced  ac- 
celerating action  upon  the  rate  of 
cure  of  rubber ;  therefore,  when  waste 
rubber  containing  free  sulphur  is 
placed  in  a  devulcanizer  of  whatever 
type,  and  the  alkaline  solution  added, 
and  the  steam  turned  on  until  a 
pressure  of  60  Ibs.  or  more  is  reached, 
there  is  every  reason  to  believe  that 
some  additional  vulcanization  is  sure 
to  take  place  although  we  are  carry- 
ing on  what  we  term  devulcaniza- 
tion. 

Then  again  it  is  imperative  that 
as  much  as  possible  of  the  alkali  be 
removed  from  the  finished  product 
either  by  washing  or  by  the  addition 
of  a  little  acid  to  neutralize  it,  for 
if  any  remains  it  exists  there  as  an 


uncontrollable  accelerator  in  what- 
ever compound  this  shoddy  may  be 
used. 

By  the  acid  process,  the  finished 
product  seems  to  oxidize  or  deterio- 
rate more  rapidly.  It  becomes  hard 
on  the  surface  and  will  easily  crack. 

It  might  be  worth  while  to  try  and 
see  what  kind  of  a  product  couid  be 
obtained  if  the  free  sulphur  was  first 
removed  from  the  ground  rubber 
waste  by  extraction  with  hot  ace- 
tone and  then  the  application  of  the 
alkali  method.  That  would  prevent 
any  further  vulcanization  during  the 
reclaiming  process. 

This  question  comes  as  a  side  issue 
to  that  of  reclaiming.  Is  it  possible 
to  recover  the  cellulose  in  a  form  or 
modification  from  the  acid  or  alkaline 
solution,  depending  upon  the  process 
used  ?  Great  volumes  of  cellulose  are 
consumed  here.  Or  could  the  soluble 
mineral  fillers  be  profitably  recovered 
from  these  solutions?  These  ques- 
tions may  be  answered  some  day  of 
course,  and  make  it  possible  to  manu- 
facture valuable  by-products  from 
materials  that  are  lost  in  the  methods 
now  used  in  reclaiming  old  rubber. 


CHAPTER  XVII 
Preparation  of  Crude  Rubber  for  Manufacturing 


The  many  processes  through  which 
crude  rubber  must  pass  before  it  is 
turned  out  into  manufactured  articles 
introduce  many  possibilities  of  its 
being  ruined,  or  if  not  ruined,  at  least 
badly  injured. 

Recall  for  a  moment  the  steps 
which  we  have  already  mentioned, 
through  which  this  material  has 
passed ;  also  the  different  persons  who 
have  been  directly  responsible  for  its 
real  value.  Is  it  not  to  be  marveled 
at  that  we  get  as  good  results  as  we 
do?  The  development  of  plan- 
tations under  the  supervision  of 
trained  men  has  greatly  improved 
the  treatment  of  the  rubber  in  the 
earlier  stages  of  its  manufacture.  But 


even  today  the  native  of  Africa  ob- 
tains and  prepares  his  rubber  from 
the  vines  of  that  country  under  very 
crude  conditions;  the  South  Ameri- 
can produces  better  rubber ;  while  the 
plantation  rubber  is  best  of  all.  The 
manufacturer  of  today  obtains  his 
rubber  supply  from  all  sources,  rang- 
ing from  that  produced  by  the  primi- 
tive method  of  the  barbarian  tinc- 
tured with  the  tricks  of  fraudulency 
and  deceit  which  so  called  civilization 
has  taught  him,  up  to  that  produced 
by  the  more  or  less  scientific  method 
for  producing  uniform  crude  rubber. 
In  this  chapter  we  shall  follow  the 
rubber  after  it  arrives  at  the  fac- 
tory and  we  see  it  in  the  receiving 
room,  on  through  the  processes  of 


FIG.  33 — UP-RIVER  FINE  PARA  IN  FACTORY  STORAGE 
111 


112 


RUBBER    MANUFACTURE 


cleansing,  drying,  milling,  calender- 
ing, and  then  leave  it  ready  to  be 
made  up  into  whatever  article  its  par- 
ticular compound  has  been  designed 
for. 

The  Receiving  Room 

Iii  the  receiving  room,  we  find  the 
many  varieties  of  rubber  coming 
from  many  different  sources,  from 
many  different  species  of  plants,  pre- 
pared in  many  different  ways,  put 
up  in  many  different  forms  and  dif- 
ferently stored.  All  these  sorts  must 
be  put  through  the  general  proc- 
ess and  each  finds  its  own  proper 
place  in  the  finished  article  to  which 
it  is  best  adapted.  We  shall  see  there- 
fore all  the  different  shipments  each 
carrying  its  own  number  which  num- 
ber identifies  the  life  history  of  that 
particular  lot.  We  will  find  that  each 
lot  is  kept  separate  until  it  has  en- 
tered into  some  compound. 

At  certain  times  it  may  become  nec- 
essary, after  receiving  large  ship- 
ments of  rubber,  to  store  it  for  some 
length  of  time.  This  depends  a  great 
deal  upon  the  market  conditions  and 
also  the  supply  available.  When  the 
price  is  very  low,  there  is  a  tendency 
toward  large  buying  which  means 
that  it  will  be  stored  upon  arrival. 


During  certain  seasons  of  the  year  in 
normal  times,  we  find  more  rubber 
stored  than  in  certain  others.  But 
whether  stored  or  taken  from  the  re- 
ceiving room  directly,  the  first  gen- 
eral treatment  is  the  same,  namely 
that  of  cleansing  or  washing.  The 
grade  of  rubber  determines  how  and 
to  what  extent  this  process  must  be 
carried  out.  The  time  was  when  all 
rubber  brought  into  the  factory  was 
washed,  but  today  the  greater  part 
of  the  plantation  rubber  is  not 
washed,  that  having  already  been  sat- 
isfactorily done  on  the  plantation  it- 
self. A  very  small  portion  of  the 
plantation  rubber  is  washed  today  in 
the  factory,  and  only  when  it  is  used 
for  certain  special  articles  where  the 
highest  degree  of  cleanliness  is  re- 
quired. 

Washing 

The  crude  rubbers  when  taken  into 
the  wash  room  are  treated,  according 
to  the  form  in  which  they  come,  in 
different  ways.  For  instance,  if  the 
individual  pieces  are  large,  they  must 
be  cut  into  smaller  ones.  The  rubber 
is  then  soaked  in  large  tanks,  which 
contain  warm  water,  until  it  is  soft- 
ened. From  these  tanks,  the  rubber 
is  taken  to  a  machine  known  as  a 


FIG.  34 — SOAKING  TANK 


PREPARATION  OF  CRUDE  RUBBER  FOR  MANUFACTURING 


113 


' '  cracker. ' '  This  consists  of  two  cor- 
rugated rolls  turning  toward  each 
other  at  different  rates  of  speed. 
Over  these  there  is  allowed  to  flow 
warm  or  cold  water  as  is  desired, 
while  the  rubber  is  passed  between 
the  rolls.  Here  the  rubber  is  first 
torn  into  small  pieces  by  means  of  a 
more  or  less  grinding  action,  and  for 
that  reason  it  comes  through  in  a  form 
which  is  not  adherent.  In  fact  it  may 
often  be  returned  through  the  mill 
by  the  use  of  a  shovel.  Some  kinds 
of  rubber  will  remain  adherent  in  the 
form  of  a  thick  heavy  crepe.  Fine 
Para  is  of  this  variety. 

In  the  next  step  wre  find  a  varying 
practice.  In  some  factories,  this  rub- 
ber, after  passing  a  few  times  through 
the  cracker,  is  passed  to  the  adjoining 
machine  called  a  "  washer."  It  is 
like  a  cracker  in  design  but  the  cor- 
rugations of  the  rolls  are  much 
smaller,  and  the  variation  in  speed 
of  the  rolls  may  not  be  as  great. 
Here  the  rubber  is  washed  and  as- 
sumes a  thick  crepe  form.  From  here 
it  is  given  to  the  third  and  last  ma- 
chine of  similar  design  with  practi- 
cally smooth  rolls,  which  finishes  the 
washing  and  leaves  it  in  a  thin  sheet 
form. 

In  some  factories  the  rubber  goes 
through  the  cracker  and  is  then  fin- 


ished on  but  one  additional  machine. 
That,  however,  requires  the  constant 
changing  of  the  distance  between  the 
rolls,  and  introduces,  therefore,  the 
possibility  of  a  variation  in  thickness 
in  the  finished  sheets. 

Some  forms  of  rubber,  after  going 
through  the  "  cracker,"  are  washed 
in  beating  machines.  These  are  large 
oval  shaped  tanks  with  a  partition 
running  part  way  through  the  middle 
and  parallel  to  their  long  axis.  This 
partition  allows  the  passage  of  the 
charge  of  the  tank  past  both  of  its 
ends.  On  one  side  of  the  tank  is 
placed  a  rotating  cylinder  over  an  ele- 
vation in  the  floor  of  the  tank.  When 
the  rubber  is  placed  in  this  machine 
and  the  cylinder  rotated,  the  whole 
mass  will  circulate  and  pass  between 
this  drum  and  the  floor  thus  pro- 
ducing a  scrubbing  action  upon  the 
rubber.  This  form  of  washing  is 
used  with  rubbers  which  do  not  ad- 
here well  into  sheet  form. 

Special  washers  have  been  designed 
for  washing  gutta  percha  and  balata. 
These  are  washed  in  hot  water  in 
which  they  become  soft.  The  ma- 
chines used  are  automatic  to  the  ex- 
tent that  after  the  material  is  added 
and  the  machines  closed,  a  kneading 
process  under  hot  water  takes  place, 
and  the  sand,  bark  and  leaves  are  re- 


FIG.  35 — WASHING  AND  SHEETING  RUBBER 


114 


RUBBER   MANUFACTURE 


moved.  When  the  resins  are  re- 
moved from  this  washer  they  are 
sheeted  in  a  smooth  surfaced  mill. 
The  length  of  time  consumed  in 
washing  should  be  as  short  as  pos- 
sible. The  mechanical  working  of 
rubber  either  on  a  washer  or  mill 
tends  to  depolymerize  it  and  thus  re- 
duces its  nerve. 

Drying 

The  next  step  is  the  drying  of  the 
rubber.  This  is  effected  in  several  dif- 
ferent ways.  In  the  early  days  of  the 
industry,  the  sheets  of  rubber  were 
hung  in  large  rooms  which  were  kept 
rather  warm  and  the  rubber  gradually 
•dried  out.  This  required  perhaps  thirty 
days.  The  drying  room  capacity  then 
had  to  be  very  large ;  in  fact  the  mini- 
mum would  be  thirty  times  the  space 
used  each  day  if  it  required  thirty 
days  to  dry  out.  This  process  was 
slow  and  it  required  a  large  amount 
of  space.  To  hasten  this  process,  * 
therefore,  two  principles  recom- 
mended themselves.  First,  the  chang- 
ing of  the  air  in  the  drying  rooms.  As 
the  air  becomes  saturated  with  mois- 
ture, evaporation  takes  place  very 
slowly,  so  by  forced  ventilation  the 
length  of  time  of  drying  the  rubber 
was  reduced,  and  therefore  the  capac- 
ity of  the  drying  rooms  was  in- 
•creased.  Then  maintaining  these 
rooms  at  a  uniformly  moderate 


temperature  aided  materially  in  the 
drying  process.  Where  this  method 
is  used  the  rubber  is  hung  over  racks. 
The  actual  time  required  to  dry  the 
rubber  depends  also  on  the  thickness 
of  the  sheets.  As  mentioned,  it  is  a 
big  advantage  to  have  the  sheets  of 
uniform  thickness  so  that  they  will  all 
be  dried  at  the  same  time;  this  is 
attained  by  having  the  washers 
set  so  that  the  last  one  through  which 
the  rubber  passes  need  not  be 
changed.  Some  forms  of  rubber  are 
very  soft  and  in  a  warm  room  will  so 
soften  that  they  will  not  support  their 
own  weight  when  hanging  from  the 
racks.  To  overcome  this  difficulty  a 
different  practice  is  resorted  to. 

This  consists  in  removing  the  water 
more  rapidly  from  the  rubber  by  plac- 
ing it  in  a  tight  chamber  heated  with 
steam  coils  from  which  the  air  may  be 
removed.  In  other  words,  the  rub- 
ber is  dried  in  a  partial  vacuum.  The 
rubber  is  placed  upon  trays  which 
slip  into  these  vacuum  driers.  Here 
the  rubber  is  dried  in  about  three 
hours.  This  method  has  received  con- 
siderable criticism  upon  the  ground 
that  it  impairs  the  nerve  of  the  rub- 
ber, and  some  have  contended  that  it 
could  be  used  only  with  certain  grades 
of  rubber.  But  today  more  rubber  is 
vacuum  dried  than  ever  before,  indi- 
cating that  the  practice  is  here  to 
stay. 


FIG.  36 — STOCK  DRYING  ROOM 


PREPARATION  OF  CRUDE  RUBBER  FOR  MANUFACTURING 


115 


Another  process  of  drying  which 
has  been  used  in  cases  of  emergency 
is  drying  upon  the  hot  rolls  of  mills. 
For  instance,  if  the  drying  capacity 
of  a  factory  is  inadequate  to  supply 
the  required  amount  of  dry  rubber 
to  the  compound  room,  the  partially 
dried  sheets  are  removed  from  the 
drying  racks  and  taken  into  the  mill 
room.  Here  they  are  placed  upon 
large  hot  rolls,  the  moisture  in  the 
rubber  is  converted  into  vapor  and  as 
such  is  removed  from  the  rubber. 
Being  an  emergency  measure,  this  is 
resorted  to  very  seldom. 

When  the  rubber  hangs  in  drying 
rooms,  it  has  been  found  best  to  have 
the  rooms  darkened  as  the  light  seems 
not  only  to  discolor  the  rubber  but 
also  to  break  it  down  or  depolymerize 
it. 

From  the  drying  process,  the  rub- 
ber goes  to  the  compound  room  un- 
less it  has  been  vacuum  dried  and  in 
that  case,  it  is  generally  stored  for  a 
short  time. 

Mixing  Mills 

We  shall  not  discuss  the  process 
of  compounding  here  as  that  will  be 
dealt  with  in  a  future  chapter,  so  we 
next  find  the  rubber  weighed  out  in 


batches  with  different  fillers  ready  for 
the  process  of  milling,  or  incorpor- 
ating the  fillers  into  the  rubber  uni- 
formly. This  is  done  upon  mills  of 
varying  sizes.  The  rolls  are  smooth, 
and  rotate  at  different  rates  of  speed. 
Through  the  axes  of  these  rolls  hot 
and  cold  water  may  be  circulated 
either  to  warm  or  to  cool  them  as  the 
working  of  the  rubber  causes  the  rolls 
to  become  very  hot. 

The  rubber  in  the  batch  is  first 
put  upon  the  mill  and  worked  until  it 
is  ' '  broken  down  "  or  in  other  words 
becomes  soft  and  flows  evenly  over  the 
roll  and  between  the  two  rolls.  When 
this  stage  is  reached,  which  is  easily 
observed  by  the  operator,  the  fillers 
are  gradually  added  to  the  rubber 
and  are  incorporated  into  the  rub- 
ber by  returning  it  through  the  mill 
over  and  over  again. 

.Several  things  must  be  observed  in 
milling.  As  mentioned  in  connection 
with  washing,  the  mechanical  work- 
ing of  the  rubber  tends  to  depoly- 
merize it,  and  especially  is  this  true 
where  the  temperature  is  above  nor- 
mal. So  upon  the  mill  this  effect  is 
very  marked.  Therefore  it  is  de- 
sirable to  mill  the  rubber  as  rapidly 


FIG.  37 — VACUUM  DRYER 


116 


RUBBER    MANUFACTURE 


as  possible  and  yet  it  must  be  worked 
long  enough  to  make  it  an  even  or 
homogeneous  mass.  The  roll  of  the 
mill  next  to  the  operator  is  kept  a 
little  warmer  than  the  other  and  ro- 
tates at  a  slower  speed  and  for  these 
reasons  the  rubber,  while  being 
worked,  will  remain  upon  this  roll. 
Here  great  care  must  be  taken  with 
certain  compounds  especially,  for  at 
the  temperature  we  have  here,  vul- 
canization may  take  place  to  a  certain 
extent.  The  temperature  of  both  rolls 
in  a  mill  is  regulated  by  turning  on 
the  hot  or  cold  water  and  the  only 
way  the  mill  man  has  of  judging  the 
correct  temperature  is  by  the  sense 
of  touch.  "  If  it  feels  right  "  is  his 
only  guide.  There  should  be  some 
way  of  automatically  controlling  this 
temperature  by  means  of  a  thermo- 
stat. Some  experimental  work  might 
be  done  along  this  line. 

The  compounded  stocks  from  the 
mill  room  are  now  allowed  to  cool  to 
age.  Then  they  are  taken  to  the  cal- 
ender room. 

Here  the  stock  is  put  into  a ' '  warm- 
ing up  mill  "  of  the  same  type  as  is 
found  in  the  mill  room,  the  purpose 
being  to  soften  up  the  stock  again  so 
that  it  will  pass  smoothly  and  evenly 
through  the  calender.  The  calender 
is  used  to  convert  the  rubber  dough 
into  sheet  form  of  uniform  thickness 
from  which  the  majority  of  rubber 
articles  are  made. 


Most  calenders  are  of  the  three  roll 
type.  The  rubber  coming  from  the 
warming  up  mill  is  fed  between  the 
two  upper  rolls,  passes  around  the 
middle  one,  then  between  it  and  the 
lower  roll,  and  is  removed  on  the 
opposite  side  upon  a  coarse  cloth 
known  as  a  "  liner,"  which  prevents 
the  rubber  surfaces  from  adhering 
together.  For  sheeting  rubber  the 
rolls  of  the  calender  are  run  at  equal 
rates  of  speed. 

Where  friction  is  desired,  the  calen- 
der rolls  run  at  differential  speeds. 
This  gives  the  greatest  spreading 
effect. 

The  stock,  after  leaving  the  calen- 
der, is  ready  to  be  made  up  into  the 
articles  for  which  it  has  been  com- 
pounded. 

To  follow  the  rubber  from  this 
point  would  mean  to  outline  the 
manufacture  of  every  separate  article 
placed  upon  the  market.  We  have  in 
this  section  simply  given  a  general 
idea  as  to  the  handling  of  rubber  in 
its  common  processes  before  it  goes 
into  its  specialized  uses.  We  have, 
however,  only  mentioned  the  planta- 
tion rubber.  The  great  bulk  of  this 
rubber  without  being  washed  is 
brought  to  the  compound  room,  put 
into  batches,  and  taken  directly  to 
the  mill  room.  On  account  of  its  pre- 
vious treatment,  it  may  enter  the 
manufacturing  process  without  being 
washed  and  dried  in  the  factory. 


FIG.  38 — CLOSE  VIEW  OF  MIXING  MILLS 


CHAPTER  XVIII 
The  Principles  of  Compounding 


In  this  chapter  it  will  be  our  aim  to 
point  out  some  of  the  general  princi- 
ples of  compounding.  Some  of  these 
principles  are  gained  from  scientific 
experimenting  and  some  from  what  is 
commonly  called  practical  experience. 
To  say  that  more  has  been  gained 
through  one  source  than  another 
would  hardly  seem  fair,  as  each  has 
profited  from  the  other. 

The  art  of  compounding,  for  such 
it  may  be  called,  has  developed  in  the 
last  few  years  from  the  point  where 
it  was  purely  a  rule  of  thumb  to  the 
extent  that  today  men  are  trained  in 
the  science  of  compounding.  In  fact, 
we  may  go  further  and  say  that  the 
large  expenditure  of  money  in  the 
way  of  equipping  laboratories  and  in 
hiring  men  to  operate  them,  is  sim- 
ply for  the  benefit  of  the  men  who  are 
in  charge  of  the  compounding.  For 
instance,  we  may  find  in  a  laboratory 
several  men  whose  whole  time  is  given 
over  to  routine  work  in  the  test- 
ing of  crude  rubbers,  and  for  what 
reason?  That  they  may  turn  over 
some  valuable  information  to  the  com- 
pounders.  We  find  men,  too,  testing 
the  purity  of  the  pigments,  again 
to  be  of  assistance  to  the  compound- 
ers.  Today  we  find  the  large  labora- 
tories establishing  and  prosecuting 
work  of  a  research  nature  along  the 
line  of  organic  accelerators.  This, 
again,  is  done  with  the  idea  of  gaining 
some  knowledge  that  in  the  hands  of 
their  compounders  will  enable  them 
to  develop  greater  speed  in  curing 
and  thus  to  increase  production.  The 
expenditure  of  large  sums  annually 
for  research  laboratories  is  justified 
by  the  progress  made  by  the  com- 
panies which  maintain  such  labora- 
tories. 

It  matters  not  in  what  particular 


line  of  work  the  compounding  is  be- 
ing done,  the  same  problems  are  ever 
before  the  compounder,  whether  he  is 
engaged  in  compounding  tires  or  toy 
balloons.  The  following  points  are  all 
to  be  considered  and  each  given  its 
due  attention : 

1 — Quality,  including  tensile 
strength,  elasticity,  grain,  stretch,  set, 
hardness,  resistance  to  abrasion,  to 
tearing,  to  cutting,  deterioration  due 
to  ageing. 

2 — Adaptability  of  stock  to  the 
processes  through  which  it  must  pass, 
such  as  milling,  calendering  and 
spreading. 

3 — Length  of  time  and  conditions 
required  for  vulcanization. 

4 — Compatibility  with  other  stocks 
with  which  it  is  used. 

An  excellent  example  of  this  is 
found  in  the  different  stocks  which 
must  be  developed  in  the  construction 
of  a  solid  tire,  where  it  is  necessary  to 
produce  a  stock  which  will  form  a 
union  with  a  metal  base  on  one  side 
and  with  the  soft  vulcanized  tread  on 
the  other : 

5— Color. 

6 — Specific  gravity. 

7— Cost. 

We  shall  now  discuss  these  points 
as  they  bear  upon  compounding  in 
mechanical  goods,  dipped  goods,  tires 
and  hard  rubber. 

For  the  compounding  of  mechani- 
cal goods,  the  problem,  with  the  excep- 
tion of  a  few  specials,  presents  itself 
as  follows :  The  compounder  is  advised 
of  the  terms  as  called  for  by  the  speci- 
fications in  a  contract  which  includes 
price,  delivery,  specific  gravity,  color, 
and  usually  definite  tests  to  which  the 
article  must  be  subjected  and  pass. 


117 


118 


RUBBER   MANUFACTURE 


He  will,  therefore,  take  the  material 
available  and  meet  the  specifications 
with  as  much  margin  of  quality  as  the 
price  will  allow.  It  is  to  his  advan- 
tage to  make  the  time  of  cure  as  short 
as  possible  in  order  that  the  equip- 
ment may  render  the  maximum  pos- 
sible production.  Otherwise  the  con- 
ditions are  the  same  as  encountered 
in  other  stocks. 

We  shall  therefore  take  each  point 
separately  for  discussion. 

Tensile   Strength 

Tensile  strength  is  determined 
mainly  by  (a)  the  quality  of  the  rub- 
ber used;  (b)  the  balance  between  the 
rubber  and  other  compounding  in- 
gredients. This  embraces  all  there  is 
to  be  said  of  compounding  for  in 
striking  this  balance,  any  or  all  of  the 
properties  in  (1)  are  developed. 
Tensile  strength  is  acquired  mainly 
by  the  use  of  zinc  oxide  and  different 
grades  of  lampblack.  Several  other 
materials  effect  tensile  strength  more 
or  less,  but  these  two  are  in  a  class 
by  themselves. 

Resistance  to  abrasion,  to  tearing, 
to  cutting,  etc.,  are  very  much  allied 
to  tensile  strength,  although  the  latter 
is  by  no  means  a  measure  of  them. 


Zinc  oxide  is,  beyond  question  supe- 
rior to  all  other  materials  for  obtain- 
ing these  qualities,  consequently  one 
almost  never  finds  a  rubber  compound 
that  does  not  contain  zinc. 

Grain  is  another  close  ally  of  the 
properties  just  mentioned.  It  is  de- 
sirable to  produce  a  stock  which  will 
have  a  grain  that  is  more  or  less 
knotted  up  and  consequently  will  pre- 
vent easy  tearing. 

With  very  few  exceptions,  the  ad- 
dition of  other  compounding  ingredi- 
ents to  the  rubber  tend  to  cut  down 
the  strength.  In  the  case  of  certain 
materials,  such  as  inner  tubes,  sur- 
gical goods,  toy  balloons,  etc.,  the 
stretch  is  highly  desirable  and  for  this 
reason  in  their  manufacture,  very 
little  filler  may  be  used.  Such  as  are 
used  are  mainly  employed  as  color- 
ing pigments.  In  this  connection  we 
might  mention  antimony,  iron  oxide, 
arsenic  yellow,  lampblack,  litharge, 
and  various  organic  pigments. 

Occasionally  where  a  cheap  stock  is 
desired,  barytes  may  be  used  as  a 
filler  with  very  little  effect  upon  the 
stretch;  however,  in  the  majority  of 
uses  for  which  a  rubber  compound  is 
wanted,  high  stretch  is  undesirable. 


FIG.  39 — STOCK  BINS  AND  COMPOUND  BOXES 


THE  PRINCIPLES  OF  COMPOUNDING 


In  tires,  for  instance,  too  high  a  de- 
gree of  stretch  would  cause  too  much 
flexing  resulting  in  inner  friction 
which  would  cause  the  tire  to  go  to 
pieces  in  a  short  time.  No  rule  can 
be  given  for  a  proper  balance  in  re- 
gard to  this  property  since  it  must 
be  worked  out  by  actual  experiment 
in  each  individual  case. 

Elasticity 

Elasticity  is  measured  inversely  by 
the  ratio  of  the  work  done  in  stretch- 
ing to  the  work  given  back  by  the  re- 
covery. It  is  difficult  to  prophesy 
in  advance  just  how  a  compound  will 
conduct  itself  in  this  respect,  except 
that  most  cheap  fillers,  like  barytes, 
whiting,  etc.,  have  a  tendency  to  de- 
crease this  ratio. 

"  Set  "  is  nothing  but  an  approxi- 
mate measure  of  elasticity. 
Ageing  Qualities 

The  deterioration  of  rubber  articles 
upon  ageing  is  undoubtedly  one  of 
the  most  objectionable  features.  This 
deterioration  may  be  due  to  several 
factors : 

(a)  Cure,  either  over  vulcanization 
or  under  vulcanization. 

(b)  The  quantity  of  sulphur  pres- 
ent, either  excess  or  deficit. 

(c)  Oxidation,    which   may   be   in- 
fluenced   by    atmospheric    conditions 
such  as  heat,  light,  humidity,  alter- 
nate wetting  and  drying,  gases  in  the 
atmosphere,   or  in   special  cases   the 
influence  of  oils,  or  other  chemicals 
which  may  come  in  contact  with  the 
rubber  accidentally  or  of  necessity,  as 
in  the  case  where  hose  is  turned  to 
conduct  acids  or  oils.     Here  special 
compounding  is  necessary  to  produce 
a  more  resistant  compound. 

By  adaptability  to  working  on  the 
mill  or  calender,  we  mean  that  the 
compound  must  not  be  too  soft, 
neither  must  it  be  too  dry.  In  cer- 
tain cases  precaution  must  be  taken 
to  produce  stock  that  will  not  scorch 
too  readily.  Again,  in  the  case  of 
frictions,  it  is  necessary  to  produce 
the  desired  degree  of  tackiness  for 
frictioning.  In  the  tubing  machine, 
some  stocks  may  be  too  dry  and  thus 
come  through  rough ;  some  may  swell 
unevenly  after  coming  through  the 
die  of  the  tubing  machine.  Some 


stocks  will  give  trouble  due  to  bloom- 
ing when  being  calendered.  This  will 
cause  poor  unions  in  case  it  is  used  in 
laminated  fabrications.  Thus  if  the 
stock  is  soft,  either  add  some  filler  or 
remove  some  of  the  softeners.  If  too 
dry  the  reverse  of  this  will  undoubt- 
edly prove  the  remedy.  Mineral  rub- 
ber, vaseline,  pitches,  tar  and  cheap 
wild  rubbers,  and  vegetable  oils  may 
be  used  for  these  purposes. 

In  a  large  number  of  cases  it  is  nec- 
essary to  cure  two  or  more  stocks  of 
different  nature  together.  The  cure 
of  each  of  these  stocks  must  be  regu- 
lated so  that  both  will  be  cured  prop- 
erly during  the  same  length  of  time. 
We  will  take,  for  example,  solid  tire 
stocks.  Here  the  volume  of  rubber  is 
so  great  that  there  is  a  tendency  for 
the  outside  to  cure  more  rapidly  than 
the  inner  part  unless  the  time  of  vul- 
canization is  long  enough  to  permit 
the  whole  mass  to  acquire  the  same 
temperature  and  remain  at  this  tem- 
perature long  enough  so  that  the  time 
to  heat  through  and  to  cool  off  in  the 
center  will  approximately  balance. 
Then,  again,  where  tires  are  vulcan- 
ized by  the  two-cure  process,  the  car- 
cass gets  a  fair  degree  of  cure  in  the 
first  heat  but  must  retain  the  prop- 
erty of  holding  its  shape  and  at  the 
same  time  that  of  uniting  with  the 
tread  rubber  during  the  second  cure. 
The  tread  rubber  on  the  other  hand 
must  take  a  ' '  set  ' '  cure  very  quickly 
and  be  able  to  hold  its  shape  and  form 
a  union  with  that  already  in  the  car- 
cass. These  properties  may  be  ob- 
tained by  proper  manipulation  of  the 
sulphur  content  and  by  the  use  of 
suitable  accelerators. 

Co/ors 

The  next  point  is  that  of  color. 
Here  the  compounder  is  asked  either 
to  duplicate  a  certain  stock  as  to 
color  or  to  produce  a  stock  of  certain 
color.  This  is  a  point  which  is  most 
important  in  mechanical  goods.  Of 
course,  the  trade  may  become  preju- 
diced in  favor  of  a  certain  color  in 
treads  or  a  certain  color  of  inner 
tubes,  but  the  choice  is  limited  to  a 
very  few  shades,  while  in  the  case  of 
balloons,  variety  of  tints  is  to  be  de- 
sired. The  number  of  colors  available 
when  only  inorganic  fillers  were  used 


120 


RUBBER   MANUFACTURE 


restricted  the  selection  very  much,  but 
today  with  the  use  of  organic  dyes 
many  different  shades  and  tints  are 
possible.  When  compounding  to 
match  a  certain  shade,  one  often  en- 
counters difficulty  for  it  cannot  al- 
ways be  foretold  just  what  effect  the 
process  of  vulcanization  is  going  to 
have  upon  the  particular  color  pig- 
ments which  are  added,  and  especially 
is  this  true  of  certain  organic  ones. 

Specific  Gravity 

Very  often  the  compounder  is  asked 
to  produce  a  stock  of  a  certain  specific 
gravity.  This  is  done  by  having  at 
hand  a  knowledge  of  the  specific 
gravities  of  the  different  materials 
used  in  compounding.  In  this  con- 
nection we  will  give  an  example.  For 
instance,  it  is  desired  to  produce  a 
stock  having  a  specific  gravity  of  1.59. 
Let  us  assume  that  the  purpose  for 
which  this  stock  is  to  be  used  will  al- 
low the  compounder  to  use  fine  Para, 
zinc  oxide  and  sulphur.  This  is  a  very 
simple  formula  but  the  principle  may 
the  better  be  grasped  from  it.  The 
compounder  arranges  his  data  in  the 
following  manner : 


Material 
Fine  para 


Weight 
50 


is  equal  to 


5.35 


and  the  volume  of 


sulphur  is  equal  to  —   —  =  1.51.   Now 

1.98 

the  total  weight  of  the  compound  as 
taken  is  50  -f-  x  -)-  3  =  53  +  x  and 

x 
its  volume    56.1  -j-  -f-  1-51  = 

5.35 
x 
57.61    -f         — ,    and    since    Vol.    = 

5.35 
Wt.  Wt. 

-  .  • .  Sp.  gr.  =  -    — .     Wt.  = 
Sp.  gr.  Vol. 

x 


53  -f  x;  Volume^  57.61.  + 


5.35 


Thus  1.59  (the  desired  gravity)  = 
53  +  x 

57.61  + 


5.35 

Therefore  x  =  54.9  parts  of  zinc 
oxide  necessary  to  fulfill  the  above 
conditions. 

Volume  Cost 

From  the  same  problem  we  may  il- 

Specific  Cost  of 

Gravity     Volume         Cost         Weight 

.89          56.1  $.81        $40.50 


Zinc  oxide x  =  (54.9) 

Sulphur    

107.9 


5.35 

1.98 


5.35 
1.51 


.10 
.04 


5.49 
.12 


$46.11 


Conclusion 

From  his  experience  he  concludes 
that  he  will  use  50  parts  of  rubber 
with  a  specific  gravity  of  .89,  and  to 
cure  this  three  parts  of  sulphur  with 
a  gravity  of  1.98.  The  question  that 
remains  is  to  determine  the  amount 
of  zinc  oxide  necessary  to  give  the 
stock  a  gravity  of  1.59.  In  other 
words,  the  amount  of  zinc  oxide  is 
an  unknown  quantity,  but  has  a  grav- 
ity of  5.35. 

Wt. 

Now  the  volume   =  -         -  there- 

Sp.  gr. 

fore,  the  volume  of  rubber  is  equal  to 
50 
—  56.1.      The  volume  of  zinc  oxide 

.89 


lustrate  what  is  meant  by  volume 
cost  in  compounding.  Filling  in  the 
costs  and  quantity  of  zinc  oxide  in 
our  data  we  find  that  107.9  pounds  of 
this  stock  will  cost  today  $46.11, 
therefore,  the  cost  of  one  pound  will 
be  $.427.  This  stock  has  a  gravity 
of  1.59,  therefore,  a  cubic  foot  of  it 
will  weigh  62.4  (a  cubic  foot  of  water) 
times  1.59  or  99.216  pounds.  We 
have  already  determined  the  cost  per 
pound  to  be  $.427,  therefore,  the  cost 
of  a  cubic  foot  or  volume  cost,  as  it 
is  termed,  will  be  $.427  times  99.216 
or  $42.36. 

From     the     above     example     the 
method  of  compounding  with  refer- 


THE  PRINCIPLES  OF  COMPOUNDING 


121 


eiice  to  cost  will  also  be  illustrated. 
If  the  volume  cost  must  be  necessarily 
low.  then  cheap  rubber  and  pigments 
must  be  used.  If  on  the  other  hand, 
quality  is  not  to  be  sacrificed  for  cost, 
then  better  materials  may  be  em- 
ployed. In  this  connection,  however, 
a  compounder  is  able  to  save  large 
sums  of  money  for  his  company, 
where  he  is  able  to  produce  a  quality 
equal  to  or  better  than  their  com- 
petitors at  a  lower  volume  cost.  Ex- 
perience here  is  a  valuable  asset.  A 
wide  experience  and  knowledge  of 
fillers  and  rubbers,  with  a  clear  un- 
derstanding as  to  what  may  be  ac- 
complished with  each  one,  constitutes 
the  requisite  for  a  good  compounder. 
Let  us  point  out  just  a  few  of  the 
many  troubles  that  must  be  guarded 
against.  First,  some  dirt  may  get 
into  the  compound,  either  through  the 
fillers  in  their  handling,  or  in  the  rub- 
ber itself,  and  as  a  result  many  dol- 
lars '  worth  of  goods  may  be  lost.  This 
is  especially  true  in  the  case  of  com- 
pounds which  contain  a  high  rubber 
content,  like  tubes  or  band  stock.  The 
rubber  will  not  adhere  to  the  dirt 
particles  during  vulcanization,  and 
when  finished  and  the  rubber  is 
stretched  it  separates  from  the  for- 
eign body  and  this  leaves  a  hole  and 
weakens  the  goods  at  this  point. 

Second,  moisture  to  any  extent  in 
any  of  the  materials  used  in  a  stock 
is  very  objectionable.  If  moisture 
is  present  when  the  stock  goes  into 
the  vulcaiiizers  and  is  heated  above 
the  boiling  point  of  water,  this  en- 
closed moisture  will  exist  in  the  gase- 
ous condition  and  cause  "  blowing  " 
or  the  making  of  the  stock  porous. 
Again,  it  may  come  out  toward  the 
surface  and  there  cause  ' '  blistering  ' ' ; 
again,  it  may  discolor  white  stocks, 
and,  again,  if  present  in  fabric,  it  will 
cause  poor  unions  in  tire  construc- 
tion. 

Third,  if  the  fillers  contain  any 
lead  compounds  or  the  batch  pans 
from  a  previous  stock,  and  these  hap- 
pen to  find  their  way  into  what  is 
supposed  to  be  a  white  compound, 
they  will  discolor  it. 

Fourth,  great  care  must  be  exer- 
cised and  close  vigilance  kept  of  what 
is  going  on  in  the  compounding  room. 


Should  the  wrong  kind  or  the  wrong 
amount  of  material  be  used  or  a  cer- 
tain material  be  left  out  of  a  com- 
pound, it  will  be  liable  to  throw  that 
stock  out  in  cure,  color  and  gravity, 
thus  rendering  it  unfit  for  the  pur- 
pose for  which  it  was  to  be  used. 

Scorching 

Fifth,  scorching  on  the  mixing 
mills,  calender  or  tube  machines  is 
usually  due  to  forcing  the  stock  to 
run  faster  than  it  should,  too  high 
temperature,  too  much  speed  or  in- 
sufficient warming  up.  Quick  cur- 
ing stocks  especially  suffer  from  these 
causes.  The  best  way  to  get  them 
plastic  so  that  they  will  run  through 
other  processes  more  easily,  is  to  work 
thoroughly  on  the  mixing  mills  before 
any  powders  are  added,  or.  in  other 
words,  be  sure  the  rubber  is  well 
broken  down. 

Sixth,  what  is  termed  "  tough 
stock  "  is  generally  caused  from  in- 
sufficient milling  of  the  rubber  be- 
fore adding  the  fillers.  Then,  too, 
some  compounds  have  a  tendency  to 
toughen  on  long  standing.  Some 
stocks  may  come  off  from  the  mill  in 
good  condition,  but  before  the  heat, 
caused  in  mixing,  has  had  time  to 
radiate  out,  the  rubber  will  be  piled 
in  bins,  thus  trapping  the  heat,  and 
there  will  take  place  a  certain  degree 
of  vulcanization.  The  result  is  simi- 
lar to  tough  stock,  but  is  really  a 
scorched  condition. 

Seventh,  a  lumpy  stock  may  be  pro- 
duced in  several  ways.  For  instance, 
the  presence  of  dirt,  as  mentioned 
above,  may  cause  it;  or  lumps  which 
occur  in  shoddy  which  has  not  been 
evenly  reclaimed  or  refined ;  then,  too, 
the  mixing  of  tough  stock  or  scorched 
stock  with  a  soft  compound  may  be 
responsible. 

Eighth,  sulphur  bloom  on  uncured 
stock,  such  as  friction  and  cover 
stock,  may  be  due  to  using  tough  or 
scorched  stock,  insufficiently  ' '  warmed 
up  "  stock,  too  high  a  temperature 
on  the  calender,  and,  under  some  con- 
ditions, too  low  a  temperature. 

Ninth,  poor  union  of  stocks  may  be 
due  to  some  incompatibility  of  the 
stocks  to  be  joined,  improper  prepa- 
rations of  stock  in  mill  rooms,  dirt, 


122 


RUBBER   MANUFACTURE 


moisture,  soapstone,  or  anything 
which  may  affect  the  tacky  surface  of 
the  rubber,  incompletely  dried  ce- 
ment, or  poor  local  workmanship. 

Tenth,  porosity  of  the  cured  stock 
may  be  due  to  moisture  as  mentioned 
above,  insufficient  pressure,  under 
cure,  or  improper  compounding. 

Eleventh,  surface  pitting  is  closely 
related  to  porosity  or  blowing,  and  is 
caused  by  air  trapping,  surface  mois- 
ture, or  perhaps  the  same  causes 
which  produce,  porosity. 

Twelfth,  improper  cure  is  a  thing 
which  must  be  closely  watched.  If  a 
sample  is  over-cured  it  cannot  be 


brought  back,  for  the  process  of 
vulcanization  is  not  reversible,  as 
pointed  out  when  we  discussed  re- 
claiming. Over-cured  stock  may  or 
may  not  lack  in  tensile  strength,  but 
it  always  lacks  in  stretch,  is  always 
short  grain  and  ages  very  poorly.  On 
the  other  hand,  under  cure  lacks  in 
tensile  strength,  resiliency  and  gener- 
ally in  aging  properties.  Therefore, 
the  vulcanizing  must  be  closely 
checked. 

Thirteenth,  as  mentioned  above,  it 
is  difficult  to  match  certain  shades  of 
color  due  to  variations  of  materials 
used. 


CHAPTER  XIX 
Chemical  Analysis  of  Manufactured  Rubber 


In  this  chapter  we  shall  aim  to  out- 
line only  methods  which  may  be  of 
some  practical  use  to  men  in  the  lab- 
oratories. We  shall  not  attempt  to 
go  into  the  subject  to  the  extent  of 
the  complete  analysis  of  a  sample  of 
rubber,  but  shall  sketch  methods  for 
the  determination  of  facts  which  the 
man  in  charge  of  the  laboratory  is 
anxious  to  have  in  the  way  of  control 
work. 

The  first  thing  necessary  is  to  ob- 
tain a  fair  sample  of  whatever  mate- 
rial is  to  be  examined.  What  was 
said  in  a  previous  article  dealing  with 
the  chemical  analysis  of  crude  rub- 
ber in  regard  to  the  obtaining  of  a 
sample  applies  here  as  well.  Very 
often  the  stock  furnished  is  composed 
of  but  one  mix  and  in  such  cases  it 
is  a  fairly  easy  task  to  obtain  a  uni- 
form sample.  However,  when  the 
sample  submitted  is  composed  of  sev- 
eral different  mixes  and  these  have 
been  vulcanized,  thus  forming  a  com- 
pact mass,  the  problem  is  a  more  dif- 
ficult one.  As  an  example  of  the 
former  instance,  we  have  such  stocks 
as  inner  tubes  which  are  very  easily 
sampled,  while  as  an  example  of  the 
latter,  we  have  the  casing  of  an  auto 
tire.  Here  we  have  a  certain  mix  for 
the  bead,  another  for  the  friction,  an- 
other for  the  sidewall,  another  for  the 
tread,  and  still  another  for  the  cush- 
ion or  breaker.  In  the  latter  case,  the 
chemist  must  take  a  knife  and  scissors 
and  proceed  to  dissect  the  sample,  tak- 
ing out  the  different  portions  which 
represent  different  mixes.  It  takes 
some  time  and  experience  to  obtain 
good  samples  of  the  friction  espe- 
cially. 

Procedure  of  Analysis 

We  shall  now  outline  the  general 
procedure  of  analysis,  assuming  that 


the  sampling  has  been  carefully  done. 

It  is  never  necessary  to  analyze 
manufactured  rubber  for  moisture. 

The  analysis  may  be  divided  into 
two  parts,  both  of  which  may  be  run 
by  the  chemist  at  the  same  time,  the 
one  dealing  with  the  organic  mate- 
rials present  and  the  other  with  the 
inorganic. 

Determination  of  Organic  Content 

For  the  examination  of  the  organic 
content,  we  take  advantage  of  the 
action  of  different  solvents  thus  re- 
moving certain  materials  by  extrac- 
tion methods. 

To  allow  the  use  of  such  practice 
the  sample  must  first  be  reduced  to  a 
finely  divided  state  so  that  the  sol- 
vent exercises  its  maximum  effect. 
This  is  accomplished  either  by  run- 
ning the  sample  through  a  digester, 
if  it  is  of  a  nature  to  allow  this  treat- 
ment, 0]-,  as  in  the  case  of  ebonite,  it 
may  be  filed ;  but  very  often  it  is  nec- 
essary simply  to  cut  the  sample  into 
as  small  pieces  as  possible  with  the 
scissors. 

The  first  solvent  which  is  employed 
in  determining  the  organic  portion  is 
acetone.  The  acetone  used  for  this 
purpose  should  be  colorless,  and  if 
it  has  colored  upon  standing  it  should 
be  redistilled  over  potassium  carbo- 
nate before  being  used. 

A  weighed  sample  of  the  finely 
divided  rubber  is  placed  in  an  extrac- 
tion thimble  of  the  desired  type.  We 
prefer  a  Bailey-Walker  which  is  pro- 
vided with  a  Wiley  block  tin  con- 
denser. The  thimble  is  then  placed 
in  position  and  the  rubber  extracted 
with  hot  acetone  for  a  period  of  ten 
hours.  Some  have  contended  that  ten 
hours  is  not  a  sufficient  length  of 
time.  and.  of  course,  it  is  not  for  ebo- 


123 


124 


RUBBER   MANUFACTURE 


nite,  but  for  the  vast  majority  of 
cases  it  is  perfectly  safe  and  where 
exceptions  come  the  analyst  must  use 
his  own  judgment  as  to  the  proper 
length  of  time.  During  the  extraction 
the  operator  should  note  frequently 
the  general  appearance  of  the  extract. 
If  the  extract  slowly  turns  yellow 
and  has  a  slight  fluorescence  it  indi- 
cates the  presence  of  bitumens,  while 
if  it  is  strongly  fluorescent,  it  indi- 
cates coal-tar  pitch.  Mineral  oil  mani- 
fests itself  here  also  by  making  the 
extract  fluorescent  yet  it  does  not 
color  it  to  any  extent. 

When  the  extraction  is  completed, 
the  extract  is  allowed  to  cool  and  care- 
fully observed,  for  some  materials  are 
soluble  in  hot  acetone  but  crystallize 
out  on  cooling.  This  is  true  of  paraf- 
fin. The  separation  of  oily  drops 
generally  indicates  factice.  The  ex- 
tract is  now  evaporated  over  a  water 
bath  to  dryness  in  a  weighed  con- 
tainer. Here  is  the  advantage  of  the 
extraction  apparatus  mentioned  above 
—the  flask  is  of  such  size  and  shape 
that  it  can  be  weighed  and  the  ex- 
tract evaporated  to  dryness  in  it, 
while  if  a  Soxhlet  apparatus  has  been 
used  it  is  customary  to  transfer  the 
extract  to  a  smaller  tared  dish  for 
evaporating.  This  introduces  the  pos- 
sibility of  loss  and  also  the  waste  of 
acetone  in  washing  while  transferring 
from  one  flask  to  another. 

When  evaporating  to  dryness,  if 
there  is  very  much  free  sulphur  pres- 
ent, toward  the  end  of  the  process 
there  is  liable  to  take  place  very  vio- 
lent pounding  and  thus  the  loss  of 
some  of  the  residue  on  account  of  its 
being  spurted  out.  This  may  be  over- 
come to  some  extent  by  the  addition 
of  a  little  benzene  when  the  evapora- 
tion will  continue  quietly  to  dryness. 
When  the  evaporation  is  complete  the 
flask  is  dried  in  an  oven.  Some  chem- 
ists have  recommended  that  the  flask 
be  dried  in  a  hot  air  oven  for  an  hour 
at  110  cleg.  C.  while  others  claim  that 
it  is  better  to  dry  for  three  hours  at 
60  deg.  C.  The  latter  is  the  practice 
in  this  laboratory,  for  we  have  found 
that  some  of  the  rubber  resins  are 
volatile  at  110  deg.  C.  When  dried 
this  is  weighed  and  thus  the  total 
acetone  extract  is  determined  which 


in  itself  is  of  little  value.  In  this 
residue  is  to  be  found  the  free  sul- 
phur, resins,  oils  either  mineral  or 
fatty,  and  paraffin.  In  addition  to 
these  there  will  be  the  acetone  soluble 
part  of  the  factice,  or  reclaim,  or 
bitumens  and  pitches  which  might 
have  been  used  in  the  rubber  stock. 

Determination   of   Sulphur 

The  first  component  in  the  acetone 
extract  to  be  determined  is  sulphur. 
Many  methods  have  been  suggested 
and  much  discussion  has  been  given 
to  this  particular  subject.  However, 
from  a  practical  standpoint,  the  fol- 
lowing method  or  methods  give  ac- 
curate enough  results  for  control 
work  at  least. 

The  weighed  residue  in  the  flask  in 
which  we  carried  out  the  extraction, 
is  covered  with  dilute  nitric  acid 
(1-1)  and  a  cover  glass  placed  over 
the  mouth  of  the  flask,  while  it  is 
warmed  over  a  water  bath.  Care 
must  be  taken  here  that  the  reaction 
is  not  too  violent,  for  if  such  should 
happen,  some  of  the  sulphur  might 
be  lost.  After  the  first  reaction  is 
over  about  5  c.c.  of  a  saturated 
solution  of  potassium  chlorate  is 
added  and  the  solution  allowed  to 
heat  over  the  water  bath  until  the  sul- 
phur and  the  organic  matter  has  all 
disappeared.  In  some  places  the  po- 
tassium chlorate  is  added  in  the  crys- 
talline form,  but  it  is  our  experi- 
ence that  it  is  much  more  effective  as 
an  oxidizing  agent  here  if  it  is  first 
dissolved  and  its  solution  is  added. 
The  length  of  time  required  for  the 
complete  oxidation  varies  a  great 
deal  and  the  only  safe  procedure  is 
to  judge  from  the  appearance  of  the 
flask.  In  same  cases  additional  nitric 
acid  must  be  added  and  this  may  be 
the  concentrated.  In  some  instances 
where  oxidation  seems  to  be  very  dif- 
ficult, we  often  make  additions  of 
fuming  nitric  acid.  This  will  gener- 
ally complete  the  oxidation  in  a  short 
time.  The  solution  is  then  evaporated 
to  dryness  over  a  water  bath,  or  to  a 
syrup  if  that  is  as  far  as  it  will  go. 
There  is  no  danger  of  losing  any  of 
the  sulphur  by  the  volitization  of  the 
sulphuric  acid  over  a  water  bath, 
as  the  sulphur  now  exists  largely  as 
the  sulphate  of  potassium  due  to  the 


CHEMICAL  ANALYSIS  OF  MANUFACTURED  RUBBER 


125 


fact  that  potassium  chlorate  has  been 
added.  The  residue  is  now  taken  up 
in  water  to  which  a  little  hydrochloric 
acid  has  been  added,  and  if  a  clear 
solution  does  not  result  it  is  filtered 
while  cold.  The  filtrate  is  then 
brought  up  to  boiling  and  before  add- 
ing the  barium  chloride,  which  is  the 
customary  procedure,  we  are  indebted 
to  A.  C.  Carlton  for  a  slight  modifica- 
tion which  we  have  found  to  work 
beautifully  and  which  causes  the 
barium  sulphate  to  settle  very  rapidly 
in  a  granular  form  which  will  allow 
of  its  filtration  in  thirty  minutes' 
time. 

Rariurn  Sulphate  Troubles 

If  to  the  hot  filtrate  containing  the 
sulphate  you  add  10  c.c.  of  a  satu- 
rated water  solution  of  picric  acid 
and  then  the  barium  chloride  drop  at 
a  time,  then  allow  it  to  stand  until  it 
has  settled  your  troubles  with  barium 
sulphate  will  be  eliminated.  The  pic- 
ric acid  washes  out  from  the  barium 
sulphate  very  easily.  The  sulphur  is 
then  determined  in  the  usual  manner, 
by  burning  off  the  carbon  of  the  filter 
and  igniting  until  white.  The  sul- 
phur is  obtained  by  multiplying  the 
weight  of  the  barium  sulphate  by 
0.1373. 

We  have  oxidized  the  sulphur  in 
the  acetone  extract  by  the  use  of 
nitric  acid  and  bromine  and  obtained 
very  good  results.  It  has  been 
claimed  that  in  order  to  oxidize  all 
the  free  sulphur,  in  the  presence  of 
these  organic  substances,  in  addition 
to  its  nitric  acid  treatment  the  resi- 
due left  upon  evaporation  should  be 
fused  with  a  mixture  of  five  parts  of 
anhydrous  sodium  carbonate  and 
three  parts  of  potassium  nitrate.  For 
work  of  a  research  nature  this  might 
be  necessary,  but  not  for  the  work 
in  a  commercial  laboratory. 

Some  volumetric  methods  have  been 
suggested  but  we  shall  not  take  the 
space  here  to  outline  these  but  refer 
to  the  Thiocyanite  method  of  C. 
Davis  and  J.  L.  Foucar,  Jour  Soc. 
diem.  Ind.  31  (1912),  p.  100. 

Determination  of  Mineral  Oil.  Vaseline  and 
Paraffin 

The  estimation  of  mineral  oil,  vase- 
line and  paraffin  is  not  carried  out 


quantitatively  very  often.  As  stated 
above  the  appearance  of  the  acetone 
extract  furnishes  a  clue  as  to  their 
presence  and  in  actual  work  a  man's 
knowledge  of  the  stock  gives  an  idea 
as  to  the  amount  of  these  materials 
which  might  be  used.  Where  it  is  de- 
sired to  make  their  determination,  it 
is  necessary  to  extract  a  new  sample 
with  acetone  and  to  use  the  extract 
for  the  determination.  The  method 
consists  in  destroying  all  the  other 
substances  in  the  extract  except  the 
paraffin  compounds  by  the  use  of 
concentrated  sulphuric  acid.  To  ac- 
complish this,  2  c.c.  of  concentrated 
sulphuric  acid  are  added  to  the  ex- 
tract in  the  extraction  flask,  covered 
with  a  watch  glass  and  heated  in  an 
oven  for  from  three  to  four  hours  at 
a  temperature  of  110  deg.  C.  The 
contents  of  the  flask  are  then  ex- 
tracted with  petroleum  ether  several 
times  and  the  washings  transferred  to 
a  tared  flask  after  having  been  shaken 
up  in  a  separating  funnel  with  a  soda 
solution  containing  some  alcohol. 
The  petroleum  spirit  is  then  evap- 
orated off  and  the  flask  is  dried  in  an 
oven  for  two  to  three  hours  at  110 
deg.  C.,  then  weighed  and  its  percent 
determined. 

The  other  components  in  the  ace- 
tone extract  are  difficult  of  deter- 
mination and  really  do  not  add  very 
much  to  the  knowledge  of  the  sam- 
ple under  consideration. 

Some  chemists  have  led  us  to  think 
that  by  a  determination  of  the  rub- 
ber resins  in  the  acetone  extract  it  is 
possible  to  say  what  variety  of  crude 
rubber  is  used  in  the  stock.  This 
may  be  true  in  a  certain  few  cases 
where  the  resins  have  a  peculiar  odor 
which  identifies  them,  but  it  is  not 
general  enough  to  be  dependable. 

The  next  general  procedure  is  to 
gain  some  idea  as  to  the  amount  of 
bitumens  and  pitches.  The  appear- 
ance of  the  acetone  extract,  as  already 
stated,  gives  us  a  qualitative  test  as  to 
whether  or  not  these  substances  are 
present ;  but  if  there  is  a  question  as 
to  their  actual  existence  in  the  sample, 
the  following  test  may  be  applied : 

Either  some  of  the  fresh  sample 
or  some  of  the  acetone  extracted  is 
placed  in  a  test  tube  and  covered  over 


126 


RUBBER    MANUFACTURE 


with  carbon  disulphide.  and  if  either 
bitumens  or  pitches  are  present,  they 
will  be  dissolved  and  color  the  solu- 
tion ;  then  by  use  of  pyridine  as  a  sol- 
vent you  may  distinguish  between  the 
two  as  it  is  a  solvent  for  the  pitches 
but  not  for  bitumens. 

If  either  of  these  are  found  to  be 
present  the  residue  left  in  the  thimble 
from  the  acetone  extraction  is  dried 
by  allowing  it  to  remain  out  in  the 
air  when  the  acetone  will  soon  evap- 
orate, then  placed  in  an  extraction 
apparatus  and  extracted  for  several 
hours  with  carbon  disulphide ;  four 
hours  is  generally  sufficient.  The  ex- 
tract is  then  distilled  and  the  residue 
dried  in  an  oven  three  hours  at  1.10 
deg.  C.  and  the  weight  of  the  residue 
determined.  This  will  not  represent 
all  of  the  bitumens  or  pitches  as  part 
appeared  in  the  acetone  extract;  in 
fact  this  extraction  will  contain  from 
ten  to  thirty  per  cent  of  the  total 
amount  in  the  original  stock.  It  is 
plain  therefore  that  this  determina- 
tion is  of  value  only  to  the  extent  of 
giving  us  a  general  idea  as  to  the 
amount  of  these  substances  present. 
Here  again  a  man's  judgment  and 
experience  must  fill  in  the  rest. 

Determination  of  Rubber  Substitute 

The  last  experiment,  which  is  made 
upon  the  sample  for  its  organic  eon- 
tent,  is  to  ascertain  a  knowledge  of 
the  factice  or  rubber  substitute 
present. 

To  carry  out  this  advantage  is 
taken  of  the  behavior  of  these  sub- 
stances with  alkalies.  Under  the  chap- 
ter dealing  with  rubber  substitutes, 
we  pointed  out  the  fact  that  these 
materials  were  saponifiable. 

To  carry  out  this  test  successfully 
the  rubber  must  be  in  a  very  finely 
divided  state  for  the  penetrating 
power  of  the  alcoholic  potash  solution 
is  very  small. 

The  residue  left  in  the  thimble 
from  the  carbon  disulphide  extraction 
is  dried  and  in  some  cases  may  to  re- 
duced to  a  fine  powder.  It  is  then 
transferred  to  a  flask,  preferably  one 
which  has  a  ground  glass  connection 
with  a  reflux  condenser.  Then  there 
is  poured  over  the  rubber  the  alco- 
holic solution  of  potash.  Some  lab- 


oratories use  a  N/5  solution,  others 
N/l,  and  some  N/2  solution.  The 
more  concentrated  the  solution,  the 
smaller  the  amount  needed.  The  rub- 
ber is  now  boiled  in  this  solution  over 
a  water  bath  for  about  three  hours 
when  all  of  the  substitutes  should 
have  saponified  and  colored  the  so- 
lution to  some  extent,  depending  of 
course  as  to  whether  brown  or  white 
factice  has  been  used.  From  this 
point  two  procedures  have  been  used 
and  are  in  use  in  some  places  today, 
although  the  one  is  subject  to  grave 
criticism. 

We  shall  outline  the  better  method 
first.  In  this  the  solution  is  poured 
off  from  the  rubber  into  a  flask  and 
the  rubber  is  then  washed  three  or 
four  times  by  boiling  it  up  with  20 
c.c.  of  water,  each  portion  being 
added  to  the  flask  in  which  the  origi- 
nal solution  is  contained.  The  com- 
bined solutions  are  then  evaporated 
over  a  water  bath  to  a  volume  of 
about  ten  or  fifteen  cubic  centimeters. 
This  clear  solution  which  contains  the 
soap  from  the  saponification  of  the 
substitutes  is  then  transferred  to  a 
separatory  funnel,  and  when  cold 
acidified  with  either  hydrochloric  or 
sulphuric  acid  when  the  correspond- 
ing fatty  acids  will  be  liberated  from 
the  soap.  These  are  extracted  with 
ether  three  or  four  times  and  the 
ethereal  solution  evaporated  in  a  tared 
flask,  and  dried  at  110  deg.  C.  for 
an  hour.  The  weight  and  thus  the 
percent  of  factice  removed  by  this 
treatment  is  then  determined,  but  it 
must  be  remembered  that  part  of  the 
factice  was  removed  by  the  acetone 
extract;  also  that  we  are  weighing 
here  the  organic  acid  and  not  the  fac- 
tice itself,  therefore  a  correction  must 
be  made.  To  apply  this  correction, 
it  must  be  determined  whether  white 
or  brown  factice  was  used  and  to 
ascertain  this  a  test  is  made  for 
chlorine  in  the  alcoholic  potash  ex- 
tract. If  it  is  present,  while  factice 
was  used ;  otherwise  it  was  the  brown 
substitute.  To  correct,  therefore,  for 
the  white  factice,  the  amount  of  or- 
ganic acid  is  multiplied  by  1.136,  and 
if  chlorine  is  absent,  thus  indicating 
the  brown,  multiply  by  1.064.  This 
final  amount  of  factice  also  falls  short 


CHEMICAL  ANALYSIS  OF  MANUFACTURED  RUBBER 


127 


of  the  amount  actually  used  in  the 
compound  by  the  amount  that  was 
dissolved  by  the  acetone  extract.  So 
by  experiment  it  is  necessary  to  make 
another  correction  and  if  brown  sub- 
stitute was  used  the  amount  found  is 
increased  by  one-fourth,  and  needless 
to  say  this  same  amount  should  be 
subtracted  from  the  acetone  extract. 
If  white  factice  was  used,  then  an  ad- 
dition of  one-ninth  is  necessary. 

The  alternate  method  for  factice 
determination  consists  in  thoroughly 
drying  the  residue  in  the  thimble  left 
after  the  carbon  bisulphide  and 
weighing  it.  Then  subject  it  to  the 
same  alcoholic  potash  treatment  as 
mentioned  above  in  exactly  the  same 
manner.  After  effecting  the  saponi- 
fication.  the  rubber  is  filtered  on 
a  tared  paper,  washed  with  boiling 
water  several  times  before  being 
transferred  to  the  filter,  then  dried 
and  weighed.  Its  loss  in  weight  is 
taken  as  being  the  saponifiable  part 
and  thus  calculated  as  factice.  This 
method  leads  to  poor  results,  due  to 
the  fact  that  it  is  very  difficult  to 
wash  out  of  the  rubber  the  last  traces 
of  the  alkali,  but  worse  than  this,  we 
know  that  many  fillers  are  soluble  in 
strong  alkali  and  parts  of  these  will 
be  removed  and  thus  be  calculated  as 
substitutes.  Such  fillers  as  lead,  an- 
timony and  zinc  all  behave  in  this 
manner. 

There  are  certain  instances  where 
it  is  suspected  that  both  white  and 
brown  substitutes  have  been  used  in 
the  compound.  To  determine  this 
fact  a  new  alcoholic  extraction  must 
be  made  and  the  extract  is  then  evap- 
orated to  dryness;  1  c.c.  of  water  is 
added  and  then  more  heat  is  applied 
when  the  majority  of  the  organic 
matter  will  be  destroyed.  By  the  use 
of  a  spatula,  sodium  peroxide  is 
gradually  added  with  continued  heat- 
ing until  the  whole  melts.  The 
mass  is  then  allowed  to  cool  and  is 
taken  up  in  water  and  made  up  to  a 
definite  volume.  This  is  divided  and 
in  one  portion  chlorine  is  determined 
and  in  the  other  sulphur.  For  the 
chlorine  determination,  the  solution 
is  acidified  with  nitric  acid  and  the 
chlorine  precipitated  and  determined 
bv  the  addition  of  silver  nitrate. 


The  other  portion  is  acidified  with 
hydrochloric  acid  and  the  sulphur 
estimated  by  the  addition  of  barium 
chloride  in  the  manner  outlined 
above.  The  percentages  of  sulphur 
and  chlorine  in  white  substitute  do 
not  vary  much  so  that  it  is  safe  to 
calculate  for  the  amount  of  chlorine 
present  the  corresponding  amount  of 
sulphur  and  the  excess  sulphur  pres- 
ent is  a  measure  of  the  amount  of 
brown  substitute  used  in  the  com- 
pound. 

Determination  of  Rubber  Content 

This  finishes  the  analysis  of  any 
sample  for  its  organic  content  with 
the  exception  of  the  caoutchouc  hy- 
drocarbon itself.  Considerable  work 
has  been  done  with  the  idea  of  finding 
some  method  by  means  of  which  the 
rubber  proper  might  be  determined, 
but  at  present  none  of  the  methods 
suggested  allow  of  its  accurate  de- 
termination. 

The  general  practice  is  therefore 
to  arrive  at  the  rubber  content  by 
difference.  This  method  is  subject  to 
criticism  if  the  inorganic  matter  pres- 
ent is  determined  by  ashing  the  sam- 
ple, for  during  this  treatment  some 
of  the  components  are  changed  chemi- 
cally and  some  may  even  be  vola- 
tilized. 

But  now  we  are  able  to  determine 
the  inorganic  matter  by  the  use  of 
solvents  whereby  the  rubber  is  dis- 
solved and  washed  away  from  the 
pigments  with  the  aid  of  centrifugal 
machines. 

The  true  rubber  content  is  then  ar- 
rived at  by  adding  together  the  per- 
centage of  the  various  extracts,  the 
sulphur  added  for  vulcanization  and 
the  inorganic  matter  and  subtracting 
this  total  from  100.  This  method  has 
the  disadvantage  that  it  places  all 
the  errors  in  the  previous  work  upon 
the  rubber  content,  and  yet  it  gives 
results  accurate  enough  for  commer- 
cial work.  In  some  cases  the  caout- 
chouc may  be  determined  by  the  tet- 
rabromide  method  as  modified  by 
Spence.  But  too  many  other  factors 
come  in  to  cause  trouble  for  it  to  be 
regarded  as  a  reliable  method. 

The  nitrosite  method  proposed  by 
Harries  and  Alexander  is  too  long 


128 


RUBBER   MANUFACTURE 


and  too  tedious  a  method  to  recom- 
mend itself,  especially  when  the  re- 
sults are  somewhat  questionable. 

Having  dealt  in  the  last  section 
with  the  organic  portion  in  a  sample 
of  manufactured  rubber,  we  shall 
now  proceed  with  the  inorganic  part. 

Determination  of  Sulphur 

The  first  component  to  be  con- 
sidered is  sulphur  and  it  bears  a  very 
important  part.  We  have  pointed 
out  the  determination  of  the  free  sul- 
phur as  it  was  found  in  the  acetone 
extract  but  in  manufactured  rubber 
we  must  also  know  the  amount  of 
combined  sulphur.  By  this  we  mean 
the  amount  of  sulphur  in  combina- 
tion with  the  caoutchouc  itself,  for  in 
addition  to  this  we  have  sulphur  in 
combination  in  the  fillers  used,  as  in 
the  case  of  antimony,  which  is  really 
only  present  in  the  form  of  the  sul- 
phides of  antimony,  and  in  the  case 
of  lead  sulphide  which  is  formed  dur- 
ing vulcanization  when  litharge  is 
used  in  the  compound,  in  lithopone, 
as  sulphur  in  zinc  sulphide,  and  also 
here  as  the  sulphate  of  barium.  Sub- 
limed lead  also  has  sulphur  in  the 
form  of  lead  sulphate.  Then  again 
we  have  the  sulphur  which  exists  in 
factice  or  rubber  substitutes,  and  a 
little  in  mineral  rubbers.  These  rep- 
resent some  of  the  places  in  which  we 
may  expect  to  find  sulphur. 

With  these  facts  in  mind  we  pro- 
ceed to  determine  the  coefficient  of 
vulcanization  or  degree  of  vulcaniza- 
tion. To  obtain  this  knowledge,  we 
must  determine  the  total  combined 
sulphur  in  the  sample  which  we  will 
represent  by  x;  the  total  sulphur 
which  is  in  combination  with  inor- 
ganic substances  which  we  will  desig- 
nate as  y;  then  the  expression  (x-y) 
will  equal  the  amount  of  sulphur  in 
combination  with  the  rubber  proper. 

The  formula  then  which  represents 
the  degree  of  vulcanization  is  repre- 

10° ( 


sented  thus  V  — 


where  V  - 


degree  of  vulcanization,  z  =  amount 
of  caoutchouc,  which  is  generally  de- 
termined by  difference.  This  as  was 
pointed  out  before  is  liable  to  an  error 
of  several  per  cent. 


To  determine  the  x,  or  the  totally 
combined  sulphur,  it  is  necessary  to 
use  a  sample  which  has  been  subjected 
to  all  of  the  extractions,  the  acetone 
removing  the  free  sulphur,  the  car- 
bon bisulphide  removing  a  small 
amount  of  sulphur  as  it  occurs  in  the 
mineral  rubbers,  and  the  alcoholic 
potash  removing  the  sulphur  found  in 
factice. 

For  this  assay  many  methods  have 
been  suggested  but  we  shall  outline 
only  a  few  of  these. 

First  a  weighed  amount  of  the  rub- 
ber is  placed  on  the  crucible  and  cov- 
ered with  a  watch  glass  and  some 
concentrated  nitric  acid  is  added. 
When  the  violent  reaction  is  over  the 
watch  glass  is  removed,  and  the  solu- 
tion is  evaporated  to  dryness  over 
water  bath.  In  case  there  are  some 
rubber  particles  still  remaining,  the 
nitric  acid  treatment  is  repeated.  To 
the  contents  of  the  crucible  a  fusion 
mixture  of  sodium  carbonate  and  po- 
tassium nitrate  is  added  and  when 
thoroughly  mixed  is  covered  and  very 
gradually  heated.  When  the  reaction 
takes  place  it  gives  off  a  considerable 
amount  of  energy  and  therefore  the 
reaction  may  be  rather  violent. 
When  this  is  over  the  temperature  is 
raised  and  the  whole  mass  brought  to 
a  quiet  fusion  and  held  there  until  it 
appears  homogeneous.  In  some  cases 
the  fusion  is  poured  out  on  an  iron 
plate  and  when  cold  is  lixiviated  with 
water  along  with  what  remains  on 
the  crucible.  It  will  be  necessary  to 
filter  this  solution  for  it  will  have  sus- 
pended in  it  the  carbonates  of  the 
different  metallic  fillers  used.  The 
filtrate  is  acidified  with  hydrochloric 
acid  and  evaporated  to  dryness,  taken 
up  with  a  little  hydrochloric  acid  and 
water  and  again  filtered  if  necessary. 
The  sulphate  is  then  determined  as 
outlined  before. 

In  this  test  as  in  all  others,  blank 
tests  should  be  run  with  the  chemi- 
cals to  make  sure  they  are  all  free 
from  sulphur. 

Another  method  which  does  not 
take  a  long  time  and  gives  good  re- 
sults is  the  following : 

About  fifteen  grams  of  potassium 
hydroxide  are  placed  in  an  iron  or 


CHEMICAL  ANALYSIS  OF  MANUFACTURED  RUBBER 


129 


nickel  dish  with  two  c.c.  of  water  and 
heated  until  it  is  dissolved,  then  a 
weighed  amount  of  rubber  which  has 
been  extracted  is  added  and  the  heat- 
ing is  continued.  Smoke  will  be 
given  off  and  there  will  be  a  little 
sputtering  which  always  comes  when 
the  mass  is  being  stirred.  The  mass 
turns  black,  due  to  the  charring  of 
the  rubber  and  now  sodium  peroxide 
is  added  in  small  portions  until  the 
whole  mass  comes  into  a  quiet  state 
of  fusion  and  the  carbon  disappears. 
The  contents  of  the  dish  are  allowed 
to  cool  and  then  taken  up  in  water 
and  acidified  with  concentrated  hy- 
drochloric acid  until  the  iron  oxide, 
which  comes  from  the  action  of  the 
fusion  upon  the  dish,  has  dissolved. 
If  there  remains  a  white  precipitate 
it  is  probably  barium  sulphate  and 
it  may  be  filtered  off  and  weighed 
thus  getting  the  sulphur  in  it.  The 
filtrate  is  treated  for  sulphur  in  the 
usual  manner ;  then  the  two  are  added 
together.  Very  often  when  barium 
sulphate  is  precipitated  in  the  pres- 
ence of  iron  salts  there  results  con- 
siderable adsorption  of  the  iron  with 
the  result  that  when  the  barium  sul- 
phate is  ignited  it  is  colored  yellow  or 
even  reddish  brown.  In  such  a  case 
the  contents  of  the  crucible  are  dis- 
solved in  concentrated  sulphuric  acid, 
with  the  aid  of  heat  if  necessary, 
and  then  the  solution  is  poured  into 
a  beaker  of  water  when  the  barium 
sulphate  will  reprecipitate,  is  filtered 
out  and  ignited  again  when  it  will  be 
white. 

The  methods  mentioned  under  free 
sulphur  have  been  used  here  also — 
namely  oxidizing  with  concentrated 
nitric  acid  aided  either  by  potassium 
chlorate  or  bromine.  But  these 
methods  are  not  applicable  if  an  in- 
soluble sulphate  like  barium  is  pres- 
ent. These  are  the  methods  used  most 
frequently. 

The  if  in  the  above  formula  or 
the  combined  inorganic  sulphur  is 
determined  as  follows:  A  weighed 
amount  of  the  residue  obtained  by 
dissolving  away  the  rubber  from  the 
charge,  as  will  be  outlined  below,  is 
placed  in  an  iron  dish  with  about  five 
grams  of  potassium  hydroxide  and 
then  boiled  down  and  oxidized  with 


sodium  peroxide  as  outlined  above. 
The  mass  is  dissolved  in  water,  acidi- 
fied with  hydrochloric  acid  and  the 
process  is  continued  as  outlined 
above.  This  will  give  the  sulphur 
inorganically  combined  which  taken 
from  the  totally  combined  sulphur 
gives  the  amount  in  union  with  the 
caoutchouc  which  multiplied  by  100 
and  divided  by  the  amount  of  caout- 
chouc gives  the  degree  of  vulcaniza- 
tion. 

Analysis   of  Mineral   Matter 

For  the  analysis  of  the  mineral 
matter  which  was  put  into  the  com- 
pound the  old  incineration  method  is 
unreliable. 

The  best  method  today  consists  in 
placing  from  0.5  to  1.0  gram  of  the 
rubber  in  a  weighed  centrifuge  tube 
about  five  inches  long  and  an  inch  in 
diameter.  The  rubber  is  then  treated 
with  from  10  to  15  c.c.  of  a  distillate 
obtained  from  petroleum  having  a 
boiling  point  around  200  deg.  C.  or 
a  little  higher.  The  tube  is  fitted 
with  an  air  condenser  about  two  feet 
long  and  then  heated  in  a  paraffin 
bath  so  that  the  solvent  just  boils. 

The  length  of  time  necessary  to  dis- 
integrate the  rubber  varies  consider- 
ably. Where  the  degree  of  vulcani- 
zation is  low  a  few  minutes  will  be 
sufficient,  but,  as  the  degree  of  vul- 
canization goes  higher,  the  time  re- 
quired to  effect  solution  is  longer.  As 
the  rubber  approaches  ebonite,  this 
method  becomes  impossible. 

When  the  solution  is  complete  it  is 
allowed  to  cool,  when  the  mineral 
matter  will  settle  and  the  supernatant 
liquid  is  decanted.  The  mineral  resi- 
due is  then  washed  with  light  petro- 
leum spirit  and  the  tube  placed  in  a 
centrifugal  machine  and  centrifuged 
until  the  supernatant  liquid  is  free 
from  solid  particles.  In  the  majority 
of  cases  this  requires  from  twenty  to 
thirty  minutes,  and  at  the  end  of  this 
time  the  mineral  matter  is  a  hard 
compact  mass  which  allows  the  liquid 
to  be  poured  or  siphoned  off 
without  loss  of  residue.  This  wash- 
ing is  repeated  several  times  and  each 
time  the  residue  must  be  broken  up 
with  a  spatula  to  enable  effective 
washing.  The  residue  is  then  dried 


130 


RUBBER   MANUFACTURE 


to  constant  weight  and  the  per  cent  of 
mineral  charge  thus  ascertained. 

The  reason  that  we  use  the  centri- 
fuge tubes  from  the  beginning  is  that 
it  saves  transferring  the  solution 
which  gives  considerable  chance  for 
error. 

From  this  point  on  we  proceed  al- 
most as  though  we  were  carrying  out 
an  inorganic  analysis.  First,  how- 
ever, we  must  carefully  inspect  the 
mineral  charge,  for  there  may  be  in 
it  fiber,  lamp  black,  etc.,  and  these 
along  with  other  materials  may  be 
identified  by  an  examination  with  a 
magnifying  glass.  Also  before  taking 
portions  for  analysis  the  whole  resi- 
due must  be  carefully  ground  and 
mixed  because  the  process  of  centri- 
fuging  has  divided  it  into  a  more  or 
less  stratified  condition,  the  heaviest 
fillers  being  thrown  out  first  and  the 
lightest  ones 'last. 

A  weighed  portion  of  the  residue 
is  now  placed  in  a  beaker  or  evap- 
orating dish  and  treated  with  dilute 
hydrochloric  acid.  Note  whether  any 
C02  or  H2S  is  given  off.  The  solu- 
tion is  evaporated  to  dryness  over  a 
water  bath  and  the  residue  moistened 
with  concentrated  hydrochloric  acid, 
again  evaporated  to  dryness  and  then 
heated  in  an  oven  at  110  deg.  C.  for 
one  hour.  Moisten  the  residue  again 
with  hydrochloric  acid,  then  add  200 
c.c.  of  water  and  bring  to  boiling, 
then  filter  on  a  tared  paper.  If 
there  is  a  large  amount  of  lead  pres- 
ent, it  may  be  necessary  to  boil  up  the 
residue  with  more  distilled  water,  fil- 
ter and  combine  the  filtrates.  The 
residue  is  dried  and  weighed.  It 
may  contain  barium  sulphate,  silica, 
carbon,  and  organic  matter.  The  resi- 
due is  then  ignited  and  weighed.  In 
the  majority  of  cases,  this  ignition 
loss  is  a  fairly  good  indication  as  to 
the  amount  of  carbon  present  unless 
the  silica  runs  high,  as  determined 
later,  in  which  case  part  of  the  loss 
is  due  to  water. 

The  residue  is  now  placed  in  a 
platinum  dish,  if  it  was  not  ignited  in 
one,  moistened  with  hydrofluoric  acid 
and  a  drop  of  sulphuric  acid  added, 
then  evaporated  to  dryness  over  a 
water  bath,  ignited  and  weighed. 
The  loss  in  weight  here,  of  course. 


represents  the  silica,  and  the  residue 
the  barium  sulphate.  In  some  cases 
this  residue  is  colored  reddish  brown 
due  to  the  presence  of  iron  which  may 
be  eliminated  as  pointed  out  above. 
Sometimes  the  residue  is  fused  with 
an  alkaline  fusion  mixture  and  then 
analyzed  in  the  usual  manner.  Thus 
the  barytes  and  siliceous  materials  are 
determined. 

The  filtrate  from  the  acid-insoluble 
is  acidified  with  hydrochloric  acid  and, 
as  far  as  rubber  fillers  are  concerned, 
when  hydrogen  sulphide  is  conducted 
into  this  solution  we  expect  to  see 
either  a  black  sulphide  of  lead  form, 
or  an  orange  one  of  antimony.  Our 
idea  as  to  which  one  is  pretty  well 
fixed  also  for  if  the  original  sample 
was  gray  or  black  we  expect  lead, 
while  we  expect  to  see  the  antimony 
if  the  stock  was  red.  Of  course  there 
are  times  when  the  above  reasoning 
does  not  hold. 

The  hydrogen  sulphide  precipitate 
is  dissolved  in  nitric  acid,  then  a  lit- 
tle sulphuric  acid  is  added  and 
the  solution  evaporated  until  fumes 
of  sulphuric  acid  appear.  The  solu- 
tion is  then  cooled,  75  c.c.  of  water 
and  25  c.c.  of  alcohol  added,  and 
allowed  to  stand  an  hour  when 
the  lead  sulphate  may  be  filtered  off, 
washed  with  water  containing  alco- 
hol, ignited  and  weighed  as  lead  sul- 
phate. 

Some  volumetric  methods  for  de- 
termination of  lead  may  also  be  used. 

The  antimony  sulphide  is  washed 
into  a  weighed  crucible  and  nitric  acid 
added,  then  evaporated  to  dryness 
over  a  water  bath.  Fuming  nitric 
acid  is  then  added,  evaporated  again, 
then  gently  heated  and  finally  ignited 
and  weighed  as  SbO... 

If  other  sulphides  beside  antimony 
are  thrown  out  of  the  acid  solution  by 
hydrogen  sulphide,  they  may  be  sepa- 
rated by  the  use  of  sodium  sulphide. 

The  filtrate  from  the  sulphides  which 
is  acid  with  hydrochloric  acid  and 
also  contains  some  hydrosulphuric 
acid,  which  during  the  hydrogen  sul- 
phide precipitation  has  reduced  the 
iron,  if  any  is  present,  to  the  ferrous 
state,  is  boiled  to  remove  the  hydro- 
gen sulphide  and  nitric  acid  is  added 


CHEMICAL  ANALYSIS  OF  MANUFACTURED  RUBBER 


131 


to  oxidize  the  iron.  During  this  boil- 
ing there  will  be  a  separation  of  sul- 
phur which  must  be  filtered  out. 
Some  ammonium  cjiloride  is  then 
added  and  the  hot  solution  made  alka- 
line Avith  ammonium  hydroxide,  The 
precipitate  which  forms  is  composed 
of  either  the  hydroxide  of  iron  or  that 
of  aluminum,  or  perhaps  both.  A 
good  idea  of  this  is  judged  from  its 
color. 

The  solution  is  filtered.  The  resi- 
due is  ignited  and  weighed  as  Ai._.0:! 
or  Fe2O3.  When  it  is  necessary  to 
actually  determine  the  amount  of  iron 
and  aluminum,  that  is  done  in  the 
usual  manner  by  dissolving  out  the 
Al.,0,  with  sodium  hydroxide.  The 
filtrate  from  the  iron  group  is  made 
alkaline  with  ammonium  hydroxide 
and  the  zinc  precipitated  as  sulphide. 
The  sulphide  of  zinc  is  very  difficult 
to  filter,  but  if  the  ammoniacal  solu- 
tion is  warmed  and  hydrogen  sulphide 
conducted  into  it,  it  comes  down  in  a 
form  which  filters  comparatively  easy 
for  zinc.  .After  the  zinc  sulphide  is 
filtered  out  and  washed  it  is  dissolved 
off  the  filter  paper  with  hydrochloric 
acid  into  a  weighed  crucible.  The 
solution  is  then  evaporated  over  a 
water  bath,  freshly  precipitated  mer- 
curic oxide  is  added,  carefully  heated 
and  ignited  to  constant  weight,  thus 
giving  the  amount  of  zinc  oxide. 

The  zinc  is  easily  determined  volu- 
metrically  by  dissolving  the  zinc  sul- 
pliide  in  dilute  hydrochloric  acid  and 
titrating  it  with  a  solution  of  potas- 
sium ferrocyanide.  which  has  been 
standardized  against  a  known  zinc 
chloride  solution,  using  uranyl  nitrate 
as  an  external  indicator.  This  gives 
very  good  results. 

The  calcium  in  the  filtrate  from  the 
zinc  is  determined  by  adding  ammo- 
nium oxalate  to  the  hot  solution.  The 
calcium  oxalate  is  filtered  off.  washed, 
ignited  to  constant  weight  and  deter- 
mined as  calcium  oxide.  The  mag- 
nesium left  after  removing  the  cal- 
L-ium  is  precipitated  in  the  coloj  solu- 
tion by  adding  disodium  hydrogen 


phosphate    and    proceeding    in    the 
usual  manner. 

Determination  of  Carbon  or  Graphite 

It  is  weighed  as  Mg2P207  and 
then  calculated  to  MgO.  This  consti- 
tutes the  general  procedure  of  analy- 
sis of  a  sample  of  manufactured  rub- 
ber. 

As  amorphous  carbon  and  graphite 
are  used  in  large  quantities  their  de- 
termination is  sometimes  required. 

One  or  two  grams  of  the  original 
rubber  is  placed  in  an  evaporating 
dish  and  covered  with  nitric  acid,  the 
dish  being  covered  with  a  watch  glass 
until  the  first  reaction  is  over,  then 
the  solution  is  evaporated  to  dryness 
over  a  water  bath.  If  any  rubber  re- 
mains the  process  is  repeated.  When 
the  rubber  has  all  disappeared,  the 
residue  is  washed  into  a  large  beaker 
and  boiled  up  with  400  c.c.  of  water. 
The  solution  is  then  filtered  through 
a  tared  filter,  washed  several  times 
with  hot  water,  then  transferred  to  a 
beaker  and  boiled  up  with  dilute  am- 
monium hydroxide  to  whicli  a  small 
amount  of  ammonium  chloride  is 
added.  The  solution  is  again  filtered 
through  the  original  tared  filter  paper 
and  washed  with  water.  The  residue 
is  again  transferred  to  a  beaker  and 
this  time  boiled  up  with  dilute  hydro- 
chloric acid,  filtered  upon  the  tared 
filter,  washed,  dried  and  weighed. 

This  residue  may  contain  mineral 
matter  which  was  insoluble  in  nitric 
acid,  ammonium  hydroxide  and  hy- 
drochloric acid.  For  instance,  bary- 
tes  and  silica  will  both  withstand  this 
treatment.  So  the  .residue  is  now 
ignited  and  the  carbon  burnt  off.  The 
weight  of  the  residue  taken  from  the 
weight  left  in  the  tared  filter  will 
give  a  very  close  approximation  to  the 
true  amount  of  carbon  used.  The 
carbon  in  the  residue  may  be  deter- 
mined accurately  by  placing  the 
dried  carbon  residue  in  a  combustion 
furnace  and  running  a  regular  car- 
bon combustion.  This  is  seldom  if 
ever  necessarv. 


CHAPTER  XX 
Physical  Testing  of  Compounded  Samples 


In  addition  to  the  chemical  analysis 
it  is  necessary  to  make  a  number  of 
physical  tests  of  compounded  samples. 

It  is  obvious  in  the  beginning  that 
not  all  the  physical  tests  known 
should  be  carried  out  on  every  sam- 
ple submitted.  For  example,  it  is 
hardly  necessary  to  test  a  solid  tire 
for  elasticity  nor  submit  a  toy  bal- 
loon to  an  abrasion  test. 

We  shall  discuss  the  following 
tests  and  the  reader  will  be  able  to 
judge  where  each  will  be  used  to 
advantage : 

1.  Tensile  strength 

2.  Elongation 

3.  Set 

4.  Hardness 

5.  Rebound 

6.  Hysteresis 

7.  Abrasion 

8.  Penetration 

9.  Tearing 

10.  Specific  Gravity 

11.  Ageing  Tests 

a.  to  heat 

b.  to  light 

c.  to  weather 

d.  to  artificial  conditions 

12.  Dielectric  Power 

13.  Viscosity 

14.  Special    Tests    for   pneumatic 

tires 

a.  Friction  test 

b.  Wearing  tests  on  test  cars 

c.  Test  tires 

15.  Special  tests  for  solid  tires 

a.  Barbeque  test 

b.  Road  tests 

No  single  one  of  the  above  tests  is 
sufficient  to  recommend  or  to  con- 
demn a  sample,  but  several  that  are 
applicable  must  be  tried  and  as  a 
result  of  all  these  one  arrives  at  a 
conclusion. 


Practically  all  of  the  above  tests 
are  to  be  carried  out  in  a  laboratory 
and  therefore  they  are  all  more  or 
less  artificial.  By  this  we  mean  that 
we  are  not  subjecting  the  sample  to 
the  actual  conditions  under  which 
the  rubber  will  be  used  but  we  try 
to  approach  these  conditions  and 
from  the  results  obtained  speculate 
as  to  how  that  rubber  will  conduct 
itself  under  the  conditions  for  which 
it  was  designed. 

Of  course  the  most  valuable  test  to 
which  we  can  put  any  compound  is 
to  try  it  out  where  it  is  to  be  actu- 
ally used,  but  such  tests  consume  too 
much  time  before  results  are  avail- 
able. Then  again  the  compounder 
wants  to  try  out  many  new  com- 
pounds, designing  them  for  special 
purposes,  and  if  it  is  possible  to  gain 
the  information  from  some  simple 
physical  tests  in  the  laboratory  it 
saves  both  time  and  money.  With 
this  understanding  we  shall  discuss 
the  above  physical  tests. 

Tensile  Strength 

The  first  in  order  is  tensile  strength 
and  here  we  find  several  conditions 
which  influence  the  results  obtained. 
For  instance,  the  kind  of  machine 
used ;  the  shape  of  the  test  pieces  and 
how  they  are  made;  the  speed  at 
which  the  load  is  applied;  the  tem- 
perature of  the  rubber  when  the  test 
is  being  made;  and  the  grain  of  the 
rubber. 

There  are  several  machines  on  the 
market  each  possessing  certain  merits. 
The  ones  in  common  use  are  the 
Scott,  Olsen,  Cooey,  Schopper  and 
Schwartz.  Due  to  certain  differences 
in  these  machines,  and  the  peculiari- 
ties of  rubber,  it  is  difficult  to  obtain 
results  which  check  well  by  using  two 
different  makes  of  machines.  The 


132 


PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


133 


Cooey  runs  a  little  more  rapidly  than 
the  Olsen,  and,  as  a  matter  of  fact, 
the  Cooey  machine  will  show  a  greater 
tensile  than  the  Olsen.  Therefore  it 


FIG.    40 — A    SCOTT    RUBBER   TESTER 

is  necessary  when  striving  to  obtain 
some  comparative  tests  to  use  the 
same  machine,  whatever  one  that 
may  be. 

The  shape  of  the  test  piece  and  the 
\vay  in  which  it  is  made  is  an  im- 
portant point  in  connection  with 
tensile  tests. 

The  two  forms  most  in  use  today 
are  the  straight  pieces,  which  are 
enlarged  at  each  end  to  allow  the 
fixing  of  the  clamps,  and  the  ring 
form.  The  American  machines  use 
largely  the  straight  pieces  while  the 
Schopper  machine  uses  the  ring  form. 
These  test  strips  are  made  either  by 
cutting  them  out  of  a  cured  sheet  by 
means  of  a  die  either  with  a  press 
or  by  striking  with  a  mallet.  In 
some  cases  the  sample  is  cured  in  a 


mold  of  the  desired  form  for  the  test 
piece.  This  latter  method  is  not  as 
satisfactory  as  the  use  of  a  die,  for 
if  there  remains  a  rind  on  the  test 
piece  after  being  removed  from  the 
mold,  it  must  be  trimmed  off,  and, 
in  so  doing,  it  is  a  very  difficult  mat- 
ter to  avoid  nicking  the  test  piece 
itself;  and  if  that  is -done  the  sam- 
ple will  fall  short  of  its  correct  ten- 
sile strength  due  to  the  tearing  which 
will  start  from  that  point. 

In  using  the  die,  care  must  be  taken 
to  keep  the  cutting  edges  sharp  and 
free  from  nicks.  It  will  also  be  found 
that  dipping  it  first  into  a  basin  con- 
taining a  little  water,  just  to  moisten 
the  cutting  edges,  will  greatly  aid  in 
the  work. 

In  connection  with  the  Schopper 
machine,  there  is  a  die  press  for  cut- 
ting out  the  rings  and  also  a  caliper 
for  determining  the  thickness  of  the 
sample.  It  is  difficult  to  obtain  the 
true  thickness  of  the  sample  unless 
it  is  made  from  stock  which  has  been 
calendered  before  curing,  for  other- 
wise it  will  varv  some.  The  width  is 


FIG.  41 


FIG.  42 


FIG.  43 


governed  by  the  die  and  is  generally 
one-quarter  of  an  inch  as  shown  by 
the  accompanying  Fig.  41. 

Fig.  42  illustrates  the  ring  test 
placed  over  the  two  pulleys  of  the 
Schopper  machine  ready  to  be  tested. 
Fig.  43  represents  the  same  ring  after 


134 


RUBBER   MANUFACTURE 


the  test  is  begun  and  the  pulleys  have 
moved  apart  a  short  distance  and  it 
will  be  observed  that  in  such  a  test 
piece,  the  outer  circumference  of  the 


ring  is  stretched  more  than  the  inner 
circumference,  or  in  other  words  it 
is  under  a  greater  strain  than  the 
inner  and  consequently  the  ring  will 
fall  short  of  its  true  tensile  due  to 
tearing.  This  is  the  greatest  objec- 
tion to  the  ring  form. 

The  accompanying  figures  will 
illustrate  the  straight  test  pieces. 
Fig.  44  is  termed  the  short  one-half 
inch  strip  and  is  used  with  very 
elastic  stocks  which  will  not  break 
in  the  range  of  the  machine.  Fig.  45 
is  the  one-fourth  inch  die  and  is  used 
with  stocks  which  have  a  high  tensile. 
Fig.  46  is  a  short  one-fourth  inch  die 
and  is  used  with  stocks  possessing 
both  a  high  tensile  and  a  great  elas- 
ticity. Ordinarily  a  test  piece  fails  at 
its  narrowest  point  and  thus  effects 
the  break  inside  of  the  marks  on  the 
rubber.  In  ordinary  Avork  it  has  been 
stated  by  the  Bureau  of  Standards 
that  the  small  test  pieces  will  give 
larger  values  than  the  larger  strips, 
and  in  this  connection  the  following 
data  has  been  obtained. 

Die  Used.  Tensile.  %  Elongation. 

D   %  in  ..............      2440  470 

E    %    in  ..............      2845  612 

F    %    in  ..............      2538  575 

From  these  figures  the  truth  of 
that  claim  seems  to  be  confirmed. 

To  study  the  problem  still  further. 
sixty-four  stocks  were  prepared  and 
from  each  of  these  one  i/4-inch  die, 
Fig.  45,  was  cut  and  one  ^-inch, 
Fig.  44,  was  taken.  Then  each  strip 
was  tested  in  the  same  machine. 
There  were  forty-nine  instances 


FIG.  47 


where  the 


gave  a  tensile  of 


100  pounds  or  more  greater  than  the 
^-inch  piece,  thirty-three  cases  where 
the  14-inch  piece  proved  that  much 


FIG.  48 

the  better,  and  forty-six  cases  where 
the  two  checked  within  100  pounds. 
From  this  work  it  would  seem  that 
the  differences  in  actual  results  are 
slight,  whether  the  large  or  small 
strip  is  used.  Considerable  has  been 
said  concerning  the  speed  with  which 
the  load  is  applied  during  a  test.  It 
has  been  known  for  some  time  that 
this  point  has  a  definite  influence 
upon  the  tensile  strength  of  a  stock. 
That  is  the  tensile  strength  indicated 
in  a  test  depends  to  some  extent  upon 
the  speed  with  which  the  rubber  is 
stretched. 

And  in  Bulletin  No.  38  of  the 
Bureau  of  Standards  the  results  of 
their  experiments  illustrate  that 
point  very  clearly: 

No.   1 

Speed  in  in.  per  min 

Tensile  strength  per  sq.  in .    2405 
Elongation    %  .  .- 60r> 

Xo.   12 

Speed  in  in.  per  min 5 

Tensile    1900 

Elongation     405 

No.  3 

Speed   in   in 

Tensile     375 

Elongation     340 

From  these  figures,  it  is  apparent 
that  as  the  speed  with  which  the  load 
is  applied  is  increased,  the  tensile 
strength  will  be  higher.  Of  course 
there  is  a  limit  to  this  where  increas- 
ing the  speed  will  have  no  further 
effect  upon  the  results. 

The  average  speed  adopted  for 
machines  today  is  from  twenty  to 
twenty-four  inches  per  minute  and 
this  constant  speed  will  always  give 
comparative  results,  and  that  is  what 
is  desired.  Ho\vever,  if  check  work 
is  being  done  and  different  machine? 
being  used  it  would  be  advisable  to 
take  this  factor  into  consideration. 

The  temperature  of  the  rubber 
when  the  test  is  being  made  also 


25 

45 

2690 

2720 

635 

635 

i'.~) 

45 

194(1 

1H70 

500 

400 

28 

45 

430 

465 

360 

375 

PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


135 


influences  the  results.  Here  again  the 
Bureau  of  Standards  has  given  some 
valuable  experiments.  Four  stocks 
were  made  up  and  then  test  pieces 
taken,  which  were  later  tested  at 
50°  F.,  70°  F.  and  90°  F.  Before  each 
test  was  made,  the  room  in  which  the 
work  was  done  was  maintained  at  the 
temperature  desired  for  at  least  three 
hours.  The  exact  results  of  these 
tests  may  be  found  in  the  Bulletin 
38  referred  to  above. 

First  they  found  that  the  variation 
between  50°  and  70°  was  much 
greater  than  between  70°  and  90°, 
and  as  a  result  the  Bureau  now  car- 
ries out  these  tests  at  75°  F.  This 
is  a  temperature  fortunately  that  is 
fairly  easily  maintained  in  working 
conditions. 

"  Grain  " 

When  a  sample  of  rubber  is  milled 
and  perhaps  calendered  all  in  the 
same  direction  there  results  what 
may  be  termed  "  grain."  Then  if 


FIG.  49 — OLSEN   VERTICAL  TESTING 
MACHINE 

this  sample  is  cured,  the  one  cutting 
the  test  pieces  has  the  choice  of  cut- 
ting them  parallel  with  this  grain  or 
transverse  to  it.  From  considerable 


work  done  along  this  line  it  is  plainly 
evident  that  the  direction  in  which 
the  sample  piece  is  cut  does  influence 
the  results,  therefore  when  obtaining 
comparison  upon  stocks,  care  must  be 
taken  in  this  particular.  A  theory  by 
way  of  explanation  of  the  phe- 
nomenon has  been  suggested  by  a 
friend  and  Fig.  47  illustrates  the 
arrangement  of  rubber  particles  in  a 
crude  sample  of  rubber.  The  par- 
ticles may  be  considered  as  chains 
linked  together  as  colloidal  aggre- 
gates by  fine  threads  similar  to  those 
obtained  when  a  stirring  rod  is 
dipped  into  a  glue  gel  and  then  is 
removed.  As  a  result  of  the  treat- 
ment through  which  the  rubber  has 
passed  these  chains  are  extending  in 
all  directions.  Now  during  the  mill- 
ing there  is  a  tendency  to  straighten 
out  these  chains  and  thus  bring  them 
closer  together  as  shown  by  Fig.  48. 

If  the  above  theory  has  anything 
of  truth  in  it,  we  should  expect  that 
a  test  strip  cut  longitudinally  should 
contain  more  of  the  chains  and  thus 
give  a  larger  tensile  test  than  a  strip 
cut  transversely  or  across  the  grain. 

To  test  this  point  the  Bureau  of 
Standards  prepared  four  samples, 
taking  both  longitudinal  and  trans- 
verse test  strips  from  each,  and  ob- 
tained the  following  results: 

Tensile   strength  1 

Longitudinal    2730 

Transverse    2575 

%  Elongation — 

Longitudinal    630          640          480 

Transverse    640         670          555 

Permanent    Set    after    300%    elongation 
one  minute  with  one  minute  rest. 

Longitudinal    11.2%          6%     22.1%  34.3 

Transverse 7.3  5          16.3      25.0 

From  these  figures  we  see  that  the 
tensile  strength  is  greater  in  the  lon- 
gitudinal one,  as  Avould  be  expected. 
The  permanent  set  runs  higher  in  the 
longitudinal  one  also. 

Therefore  we  must  take  into  con- 
sideration the  above  facts  when  carry- 
ing out  tensile  strength  determina- 
tions. 

In  addition  to  these  points,  a  great 
deal  of  care  and  trouble  is  caused 
by  the  jaws  which  grip  the  test  strips. 

As  the  rubber  stretches  its  cross 
section  grows  less,  therefore  a  jaw 
must  be  used  which  will  tighten  as 
the  load  is  applied. 

The  ring  form  of  course  obviates 


2 

2070 
2030 


3 

1200 
1260 


4 

880 
690 

315 
315 
for 


136 


RUBBER   MANUFACTURE 


these    troubles    for    the    rings    pull 
around  pulleys. 

One  of  the  best  forms  of  jaws  is 
that  used  by  the  Olsen  machine  where 
eccentric  disks  grip  the  rubber  and 
pull  tighter  as  the  rubber  elongates. 

The  weight  shown  by  the  machine 
should  be  indicated  by  a  lever  arm 
and  not  by  a  spring,  as  the  latter  re- 
quires calibrating  too  often. 

The  actual  determination  of  the 
tensile  strength  is  then  accomplished 
by  pulling  such  a  test  strip  whose 
exact  thickness  and  width  is  known  in 
one  of  the  machines  used  above  and 
then  calculating  and  reporting  the 
number  of  pounds  which  it  requires  to 
break  a  strip  possessing  a  cross  sec- 
tional area  of  one  square  inch. 

For  example  a  test  strip  having 
a.  thickness  of  11/64  of  an  inch  and 
a  width  of  y2  inch,  sustained  a  pull  of 
180  pounds  before  it  failed.  Its  ten- 
sile strength  is  figured  thus : 

1/2  times  11/64  =  11/128  square 
inches  cross  section  area  and  this 
pulled  180  pounds,  therefore  its  ten- 
sile strength  will  equal  1/11  of  180  — 
16.4  times  128  —  2029  pounds.  The 
elongation  test  is  generally  carried 
out  at  the  same  time  as  the  tensile 
strength  test  and  on  the  same  ma- 
chine. 

On  the  test  piece,  a  distance  of  two 
inches  is  carefully  marked  off  before 
placing  it  in  the  machine.  As  the 


load  is  applied,  the  distance  between 
the  two  marks  is  carefully  measured 
and  when  the  sample  fails  the  dis- 
tance is  recorded  in  inches.  The 
elongation  is  then  figured  as  the  per 
cent  the  original  two  inches  is  of  the 
length  it  stretched  before  rupture. 
As  an  example  the  sample  above 
elongated  11.3  inches,  therefore  its 
elongation  is  11.3/2  times  100  = 
565%.  The  ring  form  machines  are 
the  only  ones  that  possess  an  auto- 
matic device  for  recording  the  elon- 
gation and  such  an  improvement  will 
be  welcomed  for  the  other  machines. 
The  "  set  "  or  recovery  is  also 
determined  at  the  same  time  as  the 
above.  The  method  used  extensively 
has  been  to  place  the  broken  ends  of 
the  test  strip  together  and  measure 
the  distance  between  the  two  marks 
which  originally  bound  the  two- 
inch  distance  before  breaking.  The 
measurement  is  made  one  minute 
after  breaking  and  is  referred  to  as 
immediate  set  in  contrast  to  perma- 
nent set  which  is  the  more  valuable. 
The  set  is  also  calculated  in  percent 
and  represents  the  ratio  of  the  stretch 
of  the  two  inches  to  the  total  elon- 
gation. 

From  the  above  example  the  two- 
inch  marks  were  found  to  be  2.6 
inches  apart  after  rupture  and  the 
elongation  was  11.3  inches,  therefore 


the  immediate  set  is  equal  to 


11.3 
2.6  —  2 


FIG.  50 — OLSEN'S  AUTOGKAPHIC  RUBBER  TESTING  MACHINE 


PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


137 


times  100  or  5.3%.  Several  meth- 
ods have  been  tried  and  recommended 
for  ascertaining  permanent  set. 
Beadle  and  Stevens  suggest  that  the 
sample  be  stretched  400%  and  be 
held  for  twenty-four  hours,  then  re- 
leased and  measured  six  hours  later. 
This  will  give  comparable  results  if 
adhered  to  for  general  work,  but  re- 
quires too  much  time. 

In  this  as  in  immediate  set  there 
is  the  probability  that  in  many  speci- 
mens this  will  not  give  the  true  re- 
covery for  there  is  likely  to  take 
place  a  tearing  or  breaking  do\vii  of 
the  rubber  and  this  of  course  de- 
creases the  set.  Along  this  line  the 
following  experiment  was  tried: 

Half  inch  test  pieces  were  prepared 
and  then  stretched  75%  of  the  break- 
ing elongation.  That  is,  if  a  sample 
elongated  13  inches  it  was  stretched 
!).75  inches  and  held  for  one  hour, 
two  hours,  three  hours,  eight  hours, 
and  sixteen  hours.  The  set  was  meas- 
ured then  in  one  minute,  ten  minutes, 
twenty  minutes,  forty  minutes  and 
sixty  minutes  and  showed  the  fol- 
lowing: 


Time  extended. 


2    hr 

:;    hr 

8    hr 

Hi    hr. . 


1M.  10M.  20M.  40M.  60M. 
.65  .49  .49  .46  .46 
.63  .60  .50  .45 


.65 

.68 


.55 
.56 
.70 


.53 
.54 
.67 


.n^ 
.53 
.60 


.50 
.52 
.53 


As  a  result  of  this  experiment,  the 
following  method  which  is  easily  and 
rapidly  carried  out  is  to  be  recom- 
mended : 

The  sample  is  stretched  60%  of  its 
elongation  and  held  five  minutes,  then 
released  and  allowed  to  rest  for  three 
minutes.  The  sample  is  subjected  to 
this  stress  three  times,  then  allowed 
to  rest  ten  minutes  and  measurement 
made.  By  this  shorter  method  about 
98%  of  the  permanent  set  is  found. 

Hardness 

Next  in  order  of  the  physical  tests 
is  the  property  of  "  Hardness."  This 
is  a  property  very  difficult  to  define, 
which  is  possessed  by  all  samples  of 
rubber  from  the  softest  vulcanized 
rubber  on  one  hand  to  the  hardest 
vulcanite  on  the  other.  Various  in- 
struments have  been  manufactured 
and  sold  for  the  purpose  of  determin- 
ing this  property  and  yet  no  entirely 
satisfactory  instrument  is  to  be  had  at 


the  present  time.  The  general  plan 
upon  which  these  instruments  have 
been  constructed  consists  of  a  plunger 
of  some  sort  with  a  point  varying  from 
a  blunt  needle  up  to  a  foot  of  quite 
measurable  area.  The  measurement 
is  taken  of  the  depth  this  plunger  will 
sink  into  the  sample  under  a  definite 
given  load :  Or  what  amounts  to  the 
same  thing  the  measurement  of  the 
force  necessary  to  cause  the  point  of 
the  plunger  to  sink  into  the  rubber  a 
definite  depth.  Under  all  circum- 
stances such  an  instrument  should 
have  a  point  sufficiently  blunt  that 
the  surface  of  the  sample  shall  not  be 
ruptured  during  the  test. 

These  tests  are  the  measure  of  the 
penetration  by  a  blunt  point  without 
rupture  of  the  rubber.  The  "  re- 
bound ' '  may  be  considered  a  test  for 
resiliency. 

The  instrument  for  this  purpose 
consists  of  a  metal  tube  with  a  slot 
along  one  side  which  is  graduated 
from  zero  at  the  bottom  to  100  at  the 
top.  A  ball  is  placed  in  this  tube  in 
such  a  way  that  it  may  be  allowed  to 
fall  freely  through  the  tube  its  gradu- 
ated height  when  in  a  vertical  posi- 
tion. The  tube  is  put  in  place  over 
the  sample  of  rubber,  which  must  be 
resting  upon  a  firm  base,  in  such  a 
position  that  with  the  ball  resting 
free  on  the  sample  it  levels  at  zero  on 
the  scale.  The  ball  is  then  raised 
until  it  occupies  the  same  position 
with  reference  to  the  100  mark.  It  is 
then  released  and  the  distance  it  re- 
bounds is  carefully  noted.  This  test 
is  repeated  as  many  times  as  seems 
desirable  preferably  at  several  dif- 
ferent points  on  the  sample,  then  the 
average  of  these  results  is  taken. 

This  test  is  especially  valuable  on 
stocks  used  for  cushioning. 

Hysteresis 

One  phase  of  rubber  testing  which 
has  received  but  comparatively  little 
attention  and  that  quite  spasmodic,  is 
the  so  called  hysteresis  test  which 
really  has  to  do  with  the  contour  of 
the  curves  representing  the  relation 
of  the  stress  to  elongation  under  the 
conditions  of  extension  and  recovery 
on  not  only  the  first  but  also  on  re- 
peated extensions.  This  includes : 


138 


RUBBER  MANUFACTURE 


FIG.  51 — A  PLASTOMETER 

1 — The  detail  of  the  contour  of  the  re- 
spective curve. 

2 — The  area  under  each  respective 
curve  which  in  turn  represents 
the  work  required  for  extension, 
and  the  work  done  by  the  sample 
in  retracting,  the  difference  rep- 
resenting the  wrork  lost  or  hys- 
teresis loss. 

3 — The  relation  of  the  contours  and 
areas  represented  by  these  differ- 
ent curves  to  each  other.  This  of 
course  includes  the  relation  be- 
tween the  percentage  of  elonga- 
tion produced  by  the  same  load 
under  repeated  flexing  as  well  as 
the  relation  of  the  loads  required 
to  produce  the  same  elongation. 
It  also  takes  in  the  increase  in  set 
under  repeated  flexing. 

The  reason  for  the  lack  of  progress 
in  this  promising  field  becomes  quite 
evident  after  an  inspection  of  the 
necessary  prerequisite  of  test  speci- 


mens.    These  may  be  enumerated  as 
follows : 

1 — The  piece  must  be  longitudinal 
and  of  uniform  cross  section 
throughout  the  entire  length  on 
which  the  graph  is  being  recorded. 

2 — The  several  pieces  which  are  being 
compared  should  be  of  the  same 
cross  section  because  of  the  diffi- 
culties in  correcting  for  each  of 
the  infinite  number  of  individual 
points  on  the  curve  for  the  differ- 
ence thus  produced  and  the  result- 
ing difference  in  the  area  produced 
underneath. 

3 — No  portion  of  that  section  of  the 
piece  on  which  the  record  is  being 
made  can  be  subjected  to  the  ac- 
tion of  the  jaws  of  the  testirg 
machine  because  of  the  numerous 
variations  produced  by  cutting, 
tearing,  slipping,  etc. 

4 — Pieces  with  enlarged  ends  are  en- 
tirely out  of  the  question  because 
of  the  great  difference  in  percent- 
age of  ultimate  elongation  pro- 
duced in  various  increments  of 
the  length  of  the  piece  under  any 
increment  of  load.  These  differ- 
ences are  so  great  as  to  completely 
obliterate  those  characteristics 
which  are  most  sought. 

5 — Ring-shaped  pieces  are  open  to  the 
same  objection  because  of  the 
great  difference  between  the 
length  represented  by  the  inner 
and  outer  circumferences. 

The  difference  in  cross  section  be- 
tween two  pieces  of  the  same  shape 
may  be  either  corrected,  or,  in  case 
the  cross  sectional  area  is  sufficiently 
large,  the  difference  may  become  so 
small  as  to  be  negligible. 

Two  methods  of  getting  around  the 
other  difficulties  have  been  suggested 
to  the  writer.  The  one  is  to  follow 
two  marks  made  on  the  narrow  part 
of  an  ordinary  longitudinal  test  piece 
with  trammel  points  which  are  so  con- 
nected with  the  recording  device  that 
only  the  actual  increase  in  distance 
between  the  points  is  recorded.  This 
device  is  a  feature  of  the  Tinius 
Olsen  rubber  testing  machine.  It  is. 
however,  practically  impossible  to 
produce  a  smooth  curve  with  this  de- 
vice. The  other  method  is  to  attach 


PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


139 


clips  similarly  rigged,  at  the  two 
marks  on  the  piece.  This  scheme 
oft'ers  a  chance  for  good  development. 

Assuming  that  these  points  have 
been  satisfactorily  met,  let  us  proceed 
to  discuss  the  results  to  be  obtained. 

Many  men  make  much  use  of  the 
relative  general  contour  of  the  curves 
produced  in  the  ordinary  manner  by 
the  usual  testing  machines.  They 
find  themselves  able  to  check  their 
ideas  on  cure,  stiffness,  etc.,  with 
much  greater  precision.  Some  make 
a  practice  of  accurately  comparing 
several  points  on  the  curves.  It 
would  therefore  seem  highly  desir- 
able to  have  an  equation  for  the 
entire  curve  in  which  the  various  con- 
stants would  present  a  ready  and  ac- 
curate means  for  such  a  comparison. 

M.  Cheneveau  and  Heim  have  at- 
tempted such  an  equation  (Sur  I'ex- 
tensibilite  du  caoutchouc  vulcanise 
Compt.  rend.  p.  320,  Feb.  6.  1911, 
and  in  The  Rubber  Industry  reports 
of  the  London  convention  in  1911). 
M.  Cheneveau  in  Le  Caoutchouc  et  la 
Gutta  percha  has  later  retracted  his 
belief  that  the  equation  holds.  E.  L. 
Davies  published  a  short  article  (Jour. 
Ind.  to  Eng.  Chem.  VI.,  985,  1914), 
with  confirming  experiments.  In  his 
lectures  at  the  Municipal  University 
of  Akron,  Mr.  Davies  has  explained 
some  further  work  along  this  line  as 
follows : 

The  equation  does  not  seem  to  hold 
on  the  return  curve  or  on  the  curve 
for  successive  cycles  nor  has  he  been 
able  generally  to  apply  the  methods 


for  obtaining  the  constants  as  ex- 
plained by  Cheneveau  and  Heim.  A 
much  more  simple  and  accurate 
method  is  presented  through  resort- 
ing to  the  principles  of  calculus.  Fig. 
52  represents  the  ordinary  type  of 
curve : 

Assume  that  this  curve  is  repre- 
sented by  the  Cheneveau  and  Heim 
equation : 

(1)  x  =  ey-\-a  sin2  by 

dx 

-j-  =  e -\-2ab  sin  by  cos  by 

(2)  =e+absin2by 
x  =  2ab  cos  2by 


Now  if  we  remember  that 


(4)  d»= J - 

dx      e  -f-  cib  sin  2  by 


=  the  slope 


of  the  tangent  at  any  point  we  may 
draw  the  tangent  and  at  any  point 
find  its  slope  and  substitute  in  this 
equation. 

Then  again,  bearing  in  mind  that 
the  second  derivative  is  equal  to  zero 
at  the  point  of  inflexion,  if  we  are 
able  to  estimate  this  point  with  fair 
accuracy  to  be  at  the  point  repre- 
sented by  x  y',  we  have 

(5) 
(6)  or 

£, 

*      45° 

whence     o  =  -r—,  =  — r 
4y       y 

and  from  (4)  since  at  y  =  0  or  at 
y  =  2y',  sin  2  by  =  0  we  have 


dy       1 

-~=— =  slope 
dx      e 


of    the    tangent     at 


either  of  these'  points  (this  gives  an- 
other proof  of  the  correctness  of  tak- 
ing e  as  the  inverse  of  the  tangent  at 
the  origin  as  suggested  by  Cheneveau 
and  Heim). 

Again  at  the  point  of  inflexion  sin 

2  by'  =  1  whence  (8)  ^  = 


dx 


a  b 


•=  slope  of  the  tangent  at  the  point 
of  inflection  and  from  (1)  and  (-6) 


x  =  ey 


sn 


2  ^ 


FIG.  52 


140 


RUBBER    MANUFACTURE 


i 


*\ 
*  27 


wherefore 

(9)  a  =  2(x'-ey') 

We  do  not  need  any  of  this  proof 
for  a  working  basis,  but  have  simply 
to  remember  that  having  located  the 
point  of  inflection  at  x'  y'  we  can 
draw  the  tangent  at  either  the  origin 
(where  the  curve  is  apt  to  be  irregu- 
lar and  therefore  not  ordinarily  to  be 
chosen)  at  the  point  of  inflexion,  or 
at  the  point  where  the  ordinate  of  the 
point  of  inflexion  and  having  drawn 
it  determine  its  slope.  The  constants 
are  then  found  from  the  following 
simple  equations: 

a  =  2  (x'-ey') 

-  v       .  45° 
0  —  -   -f  or      — 

4?/        y 

e  —  the  inverse  of  the  slope  of  the 
tangent  at  the  origin  or  at  the  point 
where  the  ordinate  is  twice  the  ordi- 
nate of  the  point  of  inflexion. 

Or  e  may  be  determined  by  equat- 
ing — ; — =•  to  the  slope  of  the  inflexi- 
e  +  ab 

mil  tangent. 

If  we  wish  to  find  the  area  under 
the  curve  up  to  any  point  represented 
by  xp  y,,  we  may  integrate  this  equa- 
tion as  follows : 


Area  O,  (a,-p  yp),  xv,  O  =  \       ey 

y< 


JVv 
I/O 


JUv 
a  si 
y<> 


sin2  by  dy 


X=0.65*  +  2.S6s/n2  0.7* 

,X 

.X" 

^ 

X 

/• 

' 

/ 

/ 

/ 

/ 

/ 

? 

/ 

/ 

/ 

/ 

^x 

/ 

3           2           46           8          70         72        74 

FIG.  53 

The  chart  here  reproduced  was 
drawn  by  means  of  clips  attached  at 
marks  2  in.  apart  on  a  test  piece 
measuring  0.5  in.  by  0.125  in.  It  was 
drawn  on  cross  section  paper  ruled 
20  lines  to  the  inch.  Because  the  re- 
cording device  reversed  the  curve  on 
the  chart,  the  equation  becomes 

y  =  ex  +  a  sin2  bx 

The  unit  of  ordinate  0.5  in.  repre- 
sents 34  per  cent  elongation ;  the  unit 
of  abscissa  represents  167.5  Ib.  per 
sq.  in.  stress.  One  square  inch  there- 
fore represents  22.32  ft.  Ib.  of  work 
done. 

By  taking  the  point  of  inflexion  at 
x^  —  4.95   and   y,  =  4.65   and   using 
the  foregoing  equations. 
a  =  2.86 

b  =  9.10  deg.  —  0.18  radians. 
e  —  0.65 

and  the  equation  y  --  ex  -|-  a  sin-  bx 
becomes 

y  =  0.654z  +  2.86  sin2  9./.r 
Comparing  with  actual  figures  we 
get 

In  considering  these  results,  it  must 


eyp'~  ,  ay,,      sin  26t/,, 

be  remembered  that  0.05  in.  or 
chart   represents   16.75   Ib.   on   t 

2 

2              47> 

A 

Y  computed. 

V  act  ii;il.                        l>iJT.  (%). 

Al.s. 

Ibs.  per  sq.  in. 

Ord. 

%  Blong. 

Ord. 

%  Elonn. 

Klong. 

Error. 

1  =  0.5" 

167.5 

0.72 

24.0 

0.63 

2  l.C. 

8,0 

14.5 

2 

335.0 

1.58 

54.0 

1.45 

49.6 

4.4 

11.2 

8 

502.5 

2.55 

87.2 

2.47 

84.5 

2.7 

3.1 

4 

670.0 

3.61 

123.0 

3.55 

121.5 

1.5 

2.4 

5 

837.5 

4.71 

161.0 

4.70 

1  60.5 

0.5 

0.3 

(i 

1005.0 

5.80 

193.0 

5.80 

198.0 

0.0 

O.n 

7 

1172.0 

6.85 

234.0 

B.78 

232.0 

2.0 

1.2 

S 

1340.0 

7.82 

267.0 

7.68 

263.0 

4.0 

1.5 

0 

1507.5 

8.66 

296.0 

8.55 

293.0 

3.0 

1.3 

10 

1675.0 

9.36 

320.0 

!t.L'5 

316.0 

4.0 

1.3 

11 

1840.0 

9.92 

339.0 

9.85 

837.0 

2.0 

0.6 

12 

2010.0 

10.25 

351.0 

10.35 

353.0 

2.0 

0.6 

12.75 

2135.0 

11.85 

405.0 

11.70 

400.0 

5.0 

1.2 

PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


14J 


axis  or  o.4  per  cent  elongation ;  the 
maximum  difference  shown  was, 
therefore,  only  about  the  width  of  the 
mark  made  by  the  tracing  pen,  and 
that  the  recording  device  was  very 
crude. 

Integrating. 

0  .sin-  9. la: 

12.75 

xdx  +2.86 


0.65  I     x 

J 


-  9.1  xdx 


Area  = 
2 


2.86.C 


.86  sin  18.2/1' 
4  X  .18 


=  69.06 

=  69.06 

4 


=  17.26  sq.  in. 


The  area  obtained  by  means  of  the 
planimeter  on  this  area  is  not  avail- 
able to  the  writer  at  present,  but  the 
two  results  differed  by  less  than  0.1 
sq.  in. 

The  various  relations  between  the 
areas  of  the  various  loops  made  by 
the  initial  and  successive  extensions 
and  retractions  should  give  a  great 
deal  of  very  desirable  information  es- 
pecially with  regard  to  the  resiliency 
of  the  stock  and  the  rate  of  diminu- 
tion of  the  same. 

Beadle  and  Stevens  have  stated 
that  the  equation 

— L  expresses  the  relation  of  the 
log  n 

elongation  produced  by  successive  ex- 
tensions to  the  same  stress.     In  this 
equation, 
L,,  =  Elongation   at   the   end   of  the 

n  th  cycle 
L,    =  Elongation  at  the  end  of  the 

first  cycle 
log  n  =  log  of  the  number  of  cycles. 

The  same  relation  may  be  obtained 
by  plotting  these  results  on  logarith- 
mic cross  section  paper,  the  result  be- 
ing a  straight  line.  The  slope  of  this 
line  is  a  measure  of  the  cyclic  fatigue. 

Instruments  for  measuring  the 
abrasion  of  rubber  have  not  as  yet 
proved  very  successful.  The  general 


method  is  based  on  the  principle  of 
subjecting  a  weighed  sample  of  rub- 
ber to  the  wearing  action  of  a  rotating 
wheel,  having  an  emery  or  carborun- 
dum surface,  either  for  a  certain 
length  of  time  or  for  a  certain  num- 
ber of  revolutions.  The  sample  is 
then  re  weighed  and  thus  the  weight 
of  the  rubber  worn  away  is  ascer- 
tained. For  purposes  of  comparison 
it  is  generally  reported  in  volume 
loss  which  is  obtained  by  dividing  the 
weight  lost  by  the  specific  gravity  of 
the  stock.  This  test  is  of  value  with 
sole  stocks  as  it  gives  a  means  of  com- 
paring different  compounds  for  wear- 
ing purposes.  One  of  the  difficulties 
to  be  overcome  in  this  test  is  the  man- 
ner in  which  the  pressure  of  the  rub- 
ber against  the  surface  of  the  wheel 
is  to  be  controlled  and  maintained 
constant.  At  present  it  is  attempted 
to  regulate  the  pressure  by  means  of 
a  dead  weight  or  a  lever.  Although 
neither  one  is  entirely  satisfactory, 
yet  if  either  is  watched  closely  the 
conditions  can  be  kept  the  same  and 
therefore  the  results  are  comparable. 

A  test  for  the  purpose  of  learning 
something  of  the  susceptibility  of 
rubber  to  puncture  is  carried  out  on  a 
machine  for  measuring  the  force  nec- 
essary to  puncture  the  stock. 

The  instrument  is  similar  to  the 
one  used  for  testing  the  hardness  with 
the  exception  that  the  plunger  carries 
a  sharper  point  than  the  one  used 
for  gauging  the  hardness.  The  force 
necessary  to  cause  the  point  to  pene- 
trate the  rubber  is  read  directly  from 
a  dial  graduated  in  arbitrary  di- 
visions. 

No  test  with  any  degree  of  satis- 
faction has  been  devised  for  deter- 
mining the  liability  of  a  rubber  to 
tear. 

Specific  Gravity 

Specific  gravity  or  density,  in  our 
use  here  may  be  regarded  as  the 
weight  in  air  of  the  sample  divided 
.by  the  weight  of  an  equal  volume  of 
water  at  4  deg.  C.,  the  maximum  den- 
sity of  water. 

Several  general  methods  are  in  use 
for  this  purpose  but  we  shall  outline 
only  four,  namely,  hydrostatic,  floata- 
tion, pycnometer  and  Jolly  Balance. 


142 


RUBBER    MANUFACTURE 


By  the  hydrostatic  method  a  sam- 
ple of  any  shape,  is  taken,  having  a 
weight  of  not  less  than  five  grams 
and  its  weight  in  air  ascertained.  It 
is  then  suspended  by  means  of  a  fine 
wire  or  horse  hair  and  then  dipped 
into  water.  Air  bubbles  are  removed 
from  the  surface  of  the  rubber  by  go- 
ing over  it  carefully  with  a  camel's 
hair  brush.  This  is  necessary  in  all 
methods  of  determining  density.  A 
beaker  of  water  is  then  placed  on  a 
support  which  straddles  the  pan  of 
a  balance.  The  piece  of  rubber  is 
then  suspended  from  the  hook  over 
the  balance  pan  in  such  a  manner  that 
the  rubber  is  immersed  in  the  water 
when  its  exact  weight  is  obtained. 
The  weight  of  the  horse  hair  im- 
mersed in  the  water  must  be  obtained, 
then  from  the  above  procedure  we 
have  the  weight  of  the  rubber  in  air, 
plus  the  hair,  minus  the  gross  weight 
of  the  rubber  and  hair  in  water  which 
will  give  the  weight  of  the  water  dis- 
placed by  the  sample,  or  its  volume. 
Since  specific  gravity  equals  weight 
divided  by  volume,  we  have  the  neces- 
sarv  data  to  obtain  the  densitv  of  the 


sample  with  reference  to  water  at 
the  temperature  of  the  determina- 
tion. If  it  is  desired  to  make  the 
temperature  correction,  all  that  is 
necessary  is  to  multiply  the  specific 
gravity  so  found  by  the  density  of  the 
water  at  the  temperature  of  the  ex- 
periment. 

If  it  is  desired  to  obtain  the  density 
of  a  sample  lighter  than  water,  it  is 
necessary  to  use  a  sinker  and  its 
weight  under  water  of  course  being 
known,  the  process  is  similar  to  the 
one  given  above.  A  piece  of  wire 
which  is  easily  bent  around  the  rub- 
ber serves  this  purpose  very  nicely. 

The  floatation  method  is  good  for 
control  work  in  the  hands  of  inexperi- 
enced workmen  as  it  requires  no 
weighings.  It  is  based  upon  the  prin- 
ciple that  solids  having  the  same  den- 
sity as  liquids,  when  placed  in  them 
will  neither  rise  nor  sink  and  the 
density  of  the  liquid  is  obtained  by  a 
hydrometer  very  easily.  For  samples 
with  a  gravity  heavier  than  water,  the 
density  of  the  liquid  is  increased  by 
the  addition  of  solids  which  pass  into 


FIG.  55 — SCOTT  MODEL  Q  HORIZONTAL  TESTING  MACHINE 


PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


143 


solution  thus  increasing  the  density. 
Zinc  sulphate  is  used  for  such  pur- 
poses. For  instance,  it  is  desired  to 
produce  a  stock  with  a  gravity  of  1.42 
and  continue  this  for  some  time.  A 
zinc  sulphate  solution  may  be  made 
up  to  the  density  and  kept  indefinitely 
provided  that  from  time  to  time  it  is 
tested  and  corrected,  for  its  density 
will  increase  due  to  evaporation.  All 
that  is  necessary,  therefore,  to  check 
up  the  stock  is  to  cut  off  a  piece  of  the 
material,  sink  it  into  the  solution  and 
note  whether  it  sinks  or  rises.  This 
is  a  rapid  control  method  only. 

The  pycnometer  method  is  used 
largely  for  samples  that  exist  as  small 
pieces  or  powder,  for  they  must  be 
tested  as  powders.  In  some  places  the 
pycnometer  is  used  altogether  and  the 
rubber  to  be  tested  is  cut  into  narrow 
strips  so  that  they  will  enter  the  bot- 
tle. This  method  is  applicable  to 
stocks  either  heavier  or  lighter  than 
water. 

A  pycnometer  bottle  is  carefully 
cleaned,  filled  with  the  liquid  in 
which  the  density  is  to  be  determined, 
and  whose  density  is  known  and  rep- 
resented by  d.  The  filled  pycnome- 
ter is  then  carefully  weighed  and  this 
weight  is  represented  by  W.  A  cer- 
tain amount  of  the  sample  is  then 
weighed  and  is  represented  by  Wv 
This  sample  is  then  placed  in  the  pyc- 
nometer and  the  bottle  is  carefully 
filled  with  the  liquid  and  again 
weighed  and  the  weight  represented 
by  W3.  We  now  have  the  data  neces- 
sary for  the  calculation  of  the  spe- 
cific gravity  of  the  sample. 

d  equals  density  of  liquid  used. 

Wx  equals  Wt.  of  sample  in  air. 

W2  equals  Wt.  of  pycnometer  and 
liquid. 

Wo  equals  Wt.  of  pycnometer  plus 
liquid  plus  sample. 

Therefore,  the  valume  of  water  or 
liquid  displaced  is  represented  by 
W-L  plus  W2  minus  W3,  and  since  Sp. 

Wt 
gr.  equals        '   we  have  Sp.  gr.  equals 


correction  for  water,  then  we  must 
multiply  the  result  so  found  by  the 
density  of  the  liquid  at  the  tempera- 
ture of  the  experiment,  or  it  may  be 
included  in  the  above  formula  and 
it  would  stand  thus:  Sp.  gr.  equals 

Wnd 

Wx  plus  W2  minus  Ws ' 

The  Jolly  Balance  is  a  rapid 
method  for  the  determination  of  the 
specific  gravity  and  does  not  require 
the  weighing  of  the  sample  on  a  deli- 
cate balance,  thus  making  it  possible 
for  an  inexperienced  person  to  learn 
to  carry  on  this  test. 

The  zero  point  on  the  balance  must 
first  be  determined,  then  any  shape 
or  size  of  rubber  is  taken  and  placed 
in  the  upper  pan  of  the  balance  with 
the  lower  "  pan  immersed  in  water. 
The  beaker  of  water  is  then  raised 
and  lowered  until  the  disc  comes  to 
equilibrium  in  front  of  the  line 
through  the  mirror.  The  stage  is  fast- 
ened in  this  position  and  the  reading 
made  on^  the  graduated  scale.  The 
sample  is  then  removed  from  the 
upper  pan  and  placed  on  the  lower 
one,  which  allows  of  the  weighing  of 
it  under  water.  The  point  of  equi- 
librium is  again  determined  and  the 
reading  is  made.  The  zero  point 
taken  from  the  first  reading  repre- 
sents its  weight  in  air,  Wx;  the  zero 
point  taken  from  the  second  reading 
represents  its  weight  in  water,  W2; 
therefore,  Wx  minus  W2  equals  the 
water  displaced  and  Sp.  gr.  equals 

W, 


== — : —       *  . =-.     Now  if  some 

Wj  plus  W,  minus  W3 

liquid  other  than  water  were  used  or 
if  we  desire  to  make  the  temperature 


Wj  minus  W2 " 

This  may  also  be  corrected  for 
temperature  by  multiplying  the  re- 
sult thus  obtained  by  the  density  of 
water  at  the  temperature  of  the  ex- 
periment. 

Specific  gravity  has  been  and  is  of 
great  value  in  determining  the  use- 
fulness of  a  stock.  Early  in  the  in- 
dustry it  was  considered  that  the 
higher  the  density  of  a  compound,  the 
less  its  merit,  for  pure  rubber  has  a 
gravity  less  than  one,  therefore,  as 
gravity  increased  rubber  must  have 
decreased.  This  is  true  within  certain 
limits  and  today  with  the  different 
practices  of  the  compounder,  more 


144 


RUBBER   MANUFACTURE 


knowledge  of  a  stock  is  necessary  than 
simply  its  gravity. 

Artificial  Ageing  Tests 

The  process  of  vulcanization  in- 
creases the  density  of  the  stock  and 
we,  therefore,  find  that  the  specific 
gravity  of  cured  rubber  is  always 
greater  than  that  of  the  uncured 
dough. 

These  are  the  methods  in  common- 
est use  in  the  laboratories  today. 

It  is  possible  to  learn  a  great  deal 
from  the  results  of  ageing  tests.  As 
the  term  implies,  the  natural  aging 
test  requires  a  large  amount  of  time 
before  it  is  possible  to  obtain  any 
results,  therefore,  artificial  ageing 
tests  have  come  into  use.  None  of 
these  artificial  tests  give  all  that  is  to 
be  desired. 

The  one  in  largest  use  today  con- 
sists of  heat  treatment.  It  is  known 
that  vulcanization  takes  place  at  all 
temperatures,  and  that  its  rapidity 
depends  upon  the  accelerators  used 
and  also  the  compound  to  some  ex- 
tent. It  follows  then  that  if  a  sample 
is  to  be  studied  under  certain  condi- 
tions of  elevated  temperature  the 
process  of  vulcanization  is  going  to 
be  continued.  This  will  also  vary 
with  different  stocks  and  thus  com- 
parative results  from  which  to  draw 
our  conclusions  are  difficult  to  obtain. 
At  least  there  is  the  possibility  of 
being  seriously  misled. 

Another  point  of  difficulty  arises 
from  the  fact  that  heat  also  tends  to 
depolymerize  the  rubber.  This  is 
truer  of  some  varieties  than  others; 
and  is  again  a  cause  for  a  variance  of 
results. 

We  know  that  cured  stocks  tend  to 
oxidize.  An  increase  of  temperature 
always  favors  this  process,  and  it 
has  been  estimated  that  an  increase  of 
10  deg.  C.  will  double  the  speed  of 
the  reaction,  so  it  is  perfectly  clear 
that  this  influence  must  be  taken  into 
consideration.  So  we  will  mention 
two  ageing  tests  that  are  studied 
under  the  inauence  of  heat. 

The  first  was  proposed  by  Dr.  Van 
Der  Linde.  He  subjected  the  rubber 
to  a  temperature  of  232  deg.  F.  for 
a  period  of  two  hours,  thinking  that 
in  this  time  and  at  that  temperature. 


the  ultimate  cure  would  be  reached. 
Then  by  studying  the  physical  prop- 
erties of  the  sample,  such  as  its  ten- 
dency to  crack  and  its  general  appear- 
ance along  with  its  tensile  strength, 
set,  and  elongation  as  compared  with 
a  sample  not  subjected  to  the  treat- 
ment, he  was  able  to  draw  his  con- 
clusions. This  has  all  of  the  objec- 
tions mentioned  above  and  then  the 
cracking  is  only  reliable  in  stocks  that 
have  a  large  amount  of  shoddy  in 
them.  The  other  heat  treatment  test 
was  first  used  by  Dr.  Geer.  He  blew 
air  through  an  oven  held  at  a  tem- 
perature of  160  deg.  F.  When  this 
oven  had  become  constant  at  work- 
ing conditions,  several  samples  of  rub- 
ber 3/32  of  an  inch  in  thickness  were 
placed  in  it.  Three  samples  were 
removed  every  day  for  a  period  of 
two  weeks.  These  samples  were  then 
alloAved  to  stand  for  twenty-four 
hours  until  the}'  had  come  to  a  state 
of  equilibrium  and  were  then  tested 
for  tensile  strength  and  elongation. 
By  this  process  the  two  sets  of  results 
were  obtained  and  these  were  then 
plotted  upon  cross  section  paper.  The 
curves  thus  obtained  showed  very 
clearly  the  time  decay  of  the  rubber. 
These  were  always  compared  against 
a  standard  stock  which  had  been  pre- 
viously determined. 

This  test  has  the  advantage  over 
the  other  in  that  the  temperature 
employed  is  much  lower  and  thus  the 
results  of  the  criticisms  mentioned 
above  are  reduced  a  great  deal.  Then, 
too,  the  possibility  of  interpreting 
the  conclusion  from  a  cure  gives  a 
better  history  of  the  stock. 

The  cures  obtained  by  this  method 
have  been  studied  in  comparison  with 
the  ones  obtained  from  natural  ageing 
tests  with  the  same  stock,  and  a  close 
agreement  is  always  found.  Such  a 
test  has  even  been  found  to  be  of 
great  value  for  a  stock  that  is  used  in 
places  where  part  of  its  service  con- 
sists in  simply  being  stored,  such  as 
fire  hose. 

Light  Tests 

Again,  rubber  articles  have  been 
studied  under  the  influence  of  light. 
It  has  been  pointed  out  that  certain 
light  rays  injure  rubber  and  should, 
therefore,  be  a  means  of  testing  rub- 


PHYSICAL  TESTING  OF  COMPOUNDED  SAMPLES 


145 


ber.  No  doubt  the  best  test  of  this 
nature  consists  in  subjecting  the  rub- 
ber to  the  direct  action  of  the  sun's 
rays.  This  enables  one  not  only  to 
study  the  effects  upon  the  rubber  but 
also  to  draw  conclusions  in  regard  to 
pigments  used.  This  test  consumes 
too  much  time  to  be  of  any  great 
value  and  it  must  always  be  carried 
out  in  conjunction  with  a  standard 
sample.  To  shorten  the  time  for  this 
test,  high  power  artificial  lights  have 
been  tried  but  have  not  proved  sat- 
isfactory. It  is  a  difficult  thing  to 
imitate  the  white  light  given  off  by 
the  sun. 

In  carrying  out  the  test  the  sam- 
ples must  not  be  displayed  behind 
glass  which  will  cut  off  some  of  the 
rays  whose  effects  it  is  so  desirous  to 
obtain.  As  a  result  of  this  it  is  dif- 
ficult to  keep  the  temperature  constant 
so  that  comparable  results  may  be  ob- 
tained at  different  seasons  of  the  year. 
It  is  also  known  that  drafts  will  in- 
fluence the  results.  It  will  be  seen 
that  a  great  many  difficulties  lie  in 
the  way  of  this  test. 

W/eather  Exposure  Tests 
Subjecting  samples  of  rubber  to  ac- 
tual weather  conditions  is  a  very  good 
test  to  establish  one's  opinion  of  a 
certain  grade  of  stock.  During  the 
summer  months  especially,  with  fre- 
quent showers,  and  high  temperature, 
a  sample  exposed  to  the  weather  un- 
dergoes about  the  severest  test  pos- 
sible. Then  it  is  possible  to  obtain 
comparable  results,  for  two  samples 
may  be  exposed  side  by  side  and  one 
of  them  be  a  standard  against  which 
the  other  is  to  be  judged.  The  pres- 
ence of  moisture  in  the  air  profound- 
ly influences  this  test  just  as  has  been 
observed  many  times  in  the  rusting 
of  iron,  which  is  a  process  of  oxida- 
tion. A  dry  piece  of  iron  rusts  very 
slowly  if  at  all,  while  a  moist  one 
changes  rapidly.  So  it  is  with  rubber 
compounds.  It  may  be  claimed  that 
the  test  is  too  slow  but  during  the 
summer  in  two  months'  time  the  re- 
sults desired  may  be  obtained.  It  is 
true  that  accidental  compounds  in 
the  air  may  influence  the  results.  For 
instance,  if  the  samples  are  exposed 
to  the  weather  in  such  a  place  that 
they  come  in  contact  with  consider- 


able sulphur  dioxide,  as  it  is  thrown 
out  of  smokestacks,  which,  with  the 
water  in  the  air,  forms  sulphurous 
acid,  thus  in  turn  will  oxidize  to 
sulphuric  acid  and  will  produce  its 
own  effect  upon  the  sample. 

This  is  a  test,  however,  which  it  is 
good  to  use. 

To  test  rubber  by  artificial  condi- 
tions we  have  in  mind  the  carrying 
out  of  certain  tests  upon  stocks, 
which,  under  the  majority  of  circum- 
stances, they  will  not  encounter  in 
their  life  history  and  yet  to  which 
they  may  be  subjected  at  certain 
times. 

For  instance,  it  is  well  to  see  what 
effect  certain  road  oils  will  have  upon 
tread  stocks  as  the  tires  may  be  used 
in  a  locality  where  the  practice  of  oil- 
ing the  roads  is  indulged  in.  Again, 
a  machine  standing  in  a  garage  may 
have  its  tires  coming  in  contact  with 
mineral  oil  and  it  is  well  to  know 
what  result  such  treatment  will  have 
upon  the  compound  employed.  In 
other  words,  it  is  a  good  practice  to 
subject  every  stock,  as  far  as  prac- 
tical, to  artificial  conditions,  of  a 
chemical  nature  approaching  the  ac- 
tual conditions  which  the  various  ar- 
ticles will  be  subjected  to  in  use.  So 
the  number  of  such  tests  is  infinite 
and  each  workman  should  study  his 
own  problems  and  prepare  and  de- 
sign his  own  tests. 

Dielectric  Tests 

A  knowledge  of  the  dielectric 
power  of  a  stock  is  of  value  for  those 
working  with  stocks  employed  in  in- 
sulating wires  and  in  making  gloves 
for  men  handling  high  tension  wires. 
For  this  purpose  it  is  only  necessary 
to  determine  the  voltage  that  will 
break  through  a  stock  of  certain 
thickness  and  this  is  always  stated  in 
the  specifications. 

Viscosity   Tests 

Viscosity  determinations  have  been 
tried  as  a  means  of  determining  the 
degree  of  vulcanization  of  stocks,  but 
have  never  proved  to  be  of  much 
value.  It  is  a  test  which  may  be  used, 
however,  to  check  up  and  keep 
cements  uniform. 

A  very  simple  type  of  viscosimeter 
is  obtained  by  taking  a  glass  tube 


146 


RUBBER   MANUFACTURE 


about  one  meter  long  with  a  diameter 
of  ten  centimeters.  Place  a  cork  in 
one  end  and  then  fill  it  with  cement 
up  to  a  certain  mark.  By  means  of 
a  stop  watch  note  how  long  it  requires 
a  shot  to  fall  to  the  bottom.  The  time 
required  compared  with  the  time  re- 
quired for  it  to  fall  through  a  simi- 
lar column  of  a  standard  cement  gives 
the  knowledge  necessary  to  correct 
the  one  under  consideration. 

Friction  Tests 

In  the  making  of  pneumatic  tires, 
the  value  of  the  finished  product  de- 
pends a  great  deal  upon  the  friction 
employed.  It  is  imperative,  there- 
fore, that  some  test  be  made  to  learn 
the  relative  value  of  different  fric- 
tions. 

The  friction  test  is  carried  out  on 
an  ordinary  tensile  machine  which  is 
geared  so  that  it  is  possible  to  run  it 
at  such  a  rate  of  speed  that  its  jaws 
will  separate  two  inches  per  minute. 
Then  the  machine  must  be  equipped 
with  jaws  suitable  to  grip  the  fric- 
tion test  piece.  If  it  is  desired  to 
test  the  friction  in  a  tire,  a  cross  sec- 
tion of  it  is  made  just  one  inch  wide 
or  close  to  that  and  then  its  width 
carefully  gauged.  The  first  ply  of 
the  friction  is  then  separated  a  lit- 
tle distance  and  fastened  in  the  jaws 
of  the  test  machine.  The  pull  neces- 
sary to  separate  the  ply  is  then  re- 
corded on  a  chart  and  the  pounds 
necessary  to  separate  a  strip  one  inch 
wide  is  calculated.  A  friction  which 
requires  twenty  pounds  pull  to  sepa- 
rate a  ply  one  inch  wide  is  regarded 
as  satisfactory. 

Each  ply  in  the  tire  is  tested  out  by 
this  procedure. 

When  it  comes,  however,  to  test- 
ing the  merits  of  one  tire  as  com- 
pared with  another,  the  most  conclu- 
sive information  is  gained  by  put- 
ting them  on  a  machine  and  run- 
ning until  one  fails  and  then  noting 
the  mileage  covered. 

To  get  tests  of  value,  they  must  be 


tried  out  in  different  parts  of  the 
country,  thus  obtaining  different  road 
conditions.  Needless  to  say  they 
should  be  used  without  chains.  These 
actual  service  tests  on  what  is  known 
as  test  cars  have  been  of  great  aid 
in  perfecting  the  product  of  the  tire 
industry  of  today. 

Barbeque   Test 

When  it  comes  to  testing  solid  tires 
we  have  what  is  known  as  the  Bar- 
beque test.  This  test  if  properly  con- 
ducted is  of  great  service  for  it  aims 
to  give  us  knowledge  at  the  point 
most  critical  in  a  solid  tire,  namely, 
the  strength  of  the  union  between  the 
hard  rubber  base  and  the  tire  itself. 
To  carry  out  this  test,  the  tire  is  se- 
cured in  a  vise,  and,  by  means  of  a 
knife,  an  oblique  cut  is  made  through 
the  tire  down  to  the  hard  rubber 
base.  By  means  of  pulling  and  using 
the  knife  also,  a  separation  of  a  few 
inches  is  effected  so  that  it  is  possible 
to  pull  up  the  tire  proper  and  tie  a 
rope  around  it.  This  rope  is  then 
tied  to  a  scale  capable  of  recording 
the  pounds  pull  and  the  pulling  begun 
at  a  tangent  to  the  point  of  separa- 
tion. The  number  of  pounds  pull 
necessary  to  effect  this  separation  of 
tire  and  base  is  carefully  noted.  The 
United  States  specifications  require 
that  for  each  inch  of  width  at  least 
100  pounds  of  pull  will  be  required  to 
separate  it. 

This  test  has  received  severe  criti- 
cism. 

Solid  tires  are  also  studied  under 
test  cars  and  in  working  conditions. 
The  rate  of  wear  on  solid  tires  is 
measured  by  taking  the  height  of 
the  tire  from  time  to  time  and  study- 
ing it  with  reference  to  mileage.  This 
is  best  done  by  plotting  the  rate  of 
wear  against  mileage. 

It  has  not  been  our  aim  to  even 
try  to  mention  all  the  tests  possible, 
but  simply  to  give  the  reader  an  idea 
of  how  physical  tests  are  studied  and 
perhaps  to  suggest  new  lines  of  en- 
deavor in  this  field. 


APPENDIX 


The  Laboratories  and  Equipment  of  the  Municipal  University 

of  Akron 


Located  in  the  center  of  the  rubber 
manufacturing  industry  of  the  world. 
Buchtel  College,  now  a  part  of  the 
Municipal  University  of  Akron,  in 
the  fall  of  1908,  installed  among  its 
courses  the  study  of  india-rubber  and 
its  use  in  industry.  Dr.  C.  M.  Knight, 
for  thirty-eight  years  Professor  of 
Chemistry  in  this  institution,  and  to 
whom  the  present  laboratory  is  dedi- 
cated, was  the  originator  of  the 
course.  By  virtue  of  his  many  years 
of  teaching  experience  and  his  keen 
appreciation  of  the  industrial  de- 
mands of  his  city  and  country  he  had 
the  wisdom  to  launch  this  work  on 
a  basis  to  insure  success.  He  was 
of  the  firm  belief  that  it  was  better 
to  graduate  a  few  men  with  a  very 
high  standard  of  ability  than  to  turn 
out  many  with  superficial  knowledge. 

In  erecting  a  fine  building  the  foun- 
dation must  first  be  laid  with  care; 
so  in  securing  an  education  that  will 
permit  of  growth  its  foundation, 
too.  must  be  deeply  and  carefully 
laid. 

In  the  University  of  Akron  course 
one  full  year  is  first  given  to  the 
study  of  inorganic  chemistry.  The 
student  thus  becomes  familiar  with 
the  great  laws  under  which  the 
science  operates.  The  second  year 
he  studies  qualitative  analysis.  Con- 
trary to  the  requirements  of  a  great 
many  institutions,  a  full  year  of  this 
work  is  required.  A  man  has  no 
license  to  be  called  a  chemist  until 
he  is  able  to  measure  up  as  an 
analyst. 

Tn  the  third  year  the  student 
is  mature  enough,  has  technique 
enough,  and  is  sufficiently  grounded 
in  principles  to  carry  on  quantita- 
tive analysis  and  begin  organic 


chemistry.  In  this  year  he  covers 
simply  the  paraffin  series  of  hydro- 
carbons. At  the  completion  of  this, 
the  foundation  is  laid  for  the  study  of 
rubber  chemistry,  for,  in  addition  to 
having  had  chemistry,  he  has  also  had 
German  and  French,  mathematics 
and  physics,  as  well  as  courses  in 
English  and  economics.  The  fourth 
year  gives  him  the  benzene  series  of 
hydrocarbons,  rubber  chemistry  and 
advanced  practical  chemistry  if  he 
desires. 

The  Rubber  Laboratory  Equipment 

The  rubber  laboratory  is  equipped 
to  carry  out  all  of  the  chemical  ex- 
periments required  in  connection  with 
the  course.  There  is  a  rubber  washer 
and  mixing  mill  which  is  mounted 
on  a  large  concrete  base  and  driven 
by  a  motor.  Another  piece  of  ap- 
paratus is  a  steam  generator  with  an 
automatic  regulator.  This  furnishes 
the  steam  used  in  the  press  vulcan- 
izer,  and  also  the  kettle  vulcanizer. 

A  Tinius  Olsen  testing  machine 
forms  part  of  the  equipment. 

With  this  outlay,  it  is  possible  to 
carry  out  actual  work  as  the  students 
will  find  it  being  done  when  they 
step  into  a  factory  laboratory. 

Brief  Description   of  the  Course 

Each  subject  naturally  is  composed 
of  two  parts:  the  lecture  room  work, 
consisting  of  lectures,  quizzes,  re- 
ports by  students,  etc.,  and  the 
laboratory  work. 

In  the  lecture  room,  the  history  of 
the  crude  rubber  is  given'  and  then 
its  development  is  traced  into  a  great 
industry.  The  different  species  are 
studied  with  reference  to  source,  col- 


147 


148 


RUBBER   MANUFACTURE 


THE  KNIGHT  CHEMICAL  LABORATORY 


lection,  coagulation,  physical  proper- 
ties and  use. 

After  some  time  is  spent  with  the 
natural  varieties,  the  plantation  rub- 
bers are  studied.  Here  it  becomes 
necessary  to  emphasize  some  of  the 
principles  of  colloidal  chemistry,  by 
which  many  of  the  phenomena  of  rub- 
ber are  explained. 

After  a  discussion  of  the  .constitu- 
tion of  rubber,  the  different  possible 


methods  of  procuring  the  synthetic 
product  are  presented.  Methods  of 
carrying  out  both  the  chemical  and 
physical  testing  of  the  crude  rubber 
are  then  given.  This  work  completes 
the  first  half  of  our  year's  work. 

The  second  half  is  devoted  to  the 
adapting  of  this  india-rubber  to  the 
various  articles  of  manufacture. 
Here  theory  is  presented  with  the 
practical  side  as  well.  In  connection 


ONE  OF  THE  LABORATORIES 


APPENDIX 


149 


with  this  lecture  room  work,  there- 
is  running  the  parallel  laboratory 
work. 

Beginning  with  the  crude  rubbers 
we  study  their  peculiarities  and  their 


DR.  C.  M.  KNIGHT 

losses  on  being  washed,  likewise  the 
action  of  different  solvents  on  them. 
The  fractional  distillation  of  rubber 
is  also  interesting  from  a  theoretical 
point  of  view  at  least. 

Thorough  analyses  along  all  the 
different  lines  of  work  are  carried  out 
here.  We  are  of  the  opinion  that  a 
chemist  first  of  all  must  be  an  analyst 


and  capable  of  doing  consistent  work 
along  this  line.  This  is  accomplished 
in  the  first  half  year,  leaving  the  sec- 
ond to  study  compounding  and  physi- 
cal testing. 

It  should  be  stated  here  that  great 
value  to  our  men  is  obtained  from 
frequent  visits  to  the  large  factories 
here.  After  studying  the  washing  of 
rubber,  and  carrying  it  out  in  the 
laboratory,  it  is  very  helpful  to  visit 
the  wash  rooms  of  two  or  more  large 
concerns.  This  of  course,  applies  to 
all  divisions  of  the  industry  and,  with 
the  cooperation  of  the  manufacturers 
of  our  city,  we  are  able  to  study  the 
various  processes  of  manufacture  in 
their  factories. 

Two  Industrial  Fellowships 

Two  industrial  fellowships  in  the 
study  of  india-rubber  have  been 
established ;  one  by  the  Firestone  Tire 
and  Rubber  Co.,  and  the  other  by  the 
Goodyear  Tire  and  Rubber  Co. 
These  fellowships  are  awarded  to  the 
graduates  of  first  grade  chemical 
courses  anywhere.  The  Fellow  re- 
ceives three  hundred  dollars  in  money 
from  the  factory  whose  Fellowship  he 
holds.  At  the  end  of  a  year  he  enters 
the  employ  of  this  company.  The 
University  gives  him  exemption  from 
all  fees  but  in  return  requires  from 
him  a  maximum  of  twelve  hours  per 
week  in  way  of  laboratory  supervision 
or  correcting  of  note  books  or  papers. 


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